There is a school of thought that players should be in the AHL until they are 110% ready for the NHL. Although this makes sense in theory, it flies in the face of an education term known as scaffolding. Scaffolding means providing constant challenges for students while they learn at their own pace. As soon as they get one concept, they move onto a tougher one without time for mastery. This allows them to grow in all ways.
The concept of scaffolding should also be applied to player development. Instead of waiting for players to be 100% ready for the NHL, call them up early and see how they do when challenged. They may be more ready than the team thinks or they may need more time. If a player is still on their entry-level contract, they can be sent back to the AHL without repercussions. This flexibility is key as teams have about 3 years to send a player down without waivers coming into the equation.
The main argument for letting prospects overbake in the AHL is that a player can be ruined if they play in the NHL too early. Although this is a common thought, it has never been proven true. There is no evidence beyond anecdotal evidence that this is a fact, there is no hard data saying a player is ruined if they are kept in the NHL before they are 100% ready. If the player is meant to be a NHL player, they should make it. It does not matter if they get called up early and struggle at first; in the end the talent should shine through.
There is also the knowledge that players hit their prime around age 25. If a team wants to harness those years of improvement, than teams need to be willing to have young players in the NHL and allow them to learn on the job. There will be more mistakes as they learn what they can and cannot do, but that is augmented by forcing them to learn in an environment that features most of the best players in the world. The NHL is faster than the AHL, it is more skilled than the AHL. When a player shows signs of being ready for the NHL, they should be given a real shot because they may show a high aptitude for playing at a higher level.
If teams prefer to over-ripen their prospects because they is what made the Detroit Red Wings successful in the 1990s and has given them continued success into the 2000s, they are missing a chance at capitalizing on the abilities of young players because a team was too stacked to give their younger players a chance over a decade ago. Instead of living in the past, teams should look to the present and realize that building an environment around growth and learning by challenging players to constantly evolve.
Once a player makes the NHL full time, they should be continually challenged to keep evolving as a player and be challenged by the coaching staff. There is no reason why skilled players should not be penalty killers or elite defensive players. If players should be constantly presented with challenges while they work to make the NHL, there is no reason why these challenges should not continue once they have made it. Most professional athletes are egomaniacs who want to be the best. Offering new situations for a player to learn in is no different than the scaffolded approach to development prior to the player making the NHL; in fact it is an extension of it.
Players should feel as though they will continue to develop once they make the NHL. There should be an environment that encourages mistakes and understands that to properly develop players they need to be pushed and encouraged. This may be seen as a softening of how players are handled, but it is the correct route to go because no matter how high players are built up, they are still human and need to be treated as humans. It is hard to only hear criticism from one person. This does not mean having to say "you did x well, but need to work on y"; instead it can mean focussing on what has been done well and accentuating the positives, because players usually know when they screw up.
What does this all mean?
It means that the ideas about how players are best developed; out of the spotlight in the AHL, are probably wrong and that practices should be adapted to better suit what we know about players peaks and about how people learn in general. Scaffolding learning so there are always new challenges presented to players and their development is continuous, even if there are more struggles while the player adapts to a new level.
NHL teams will probably not try this of course. While it would allow them to maximize the value of entry level contracts, the fear of a player not developing to their full potential is real in teams eyes. The thing is, with the right supports players can develop to their full potential and become what they are supposed to be. Fourth line players are probably well served in the NHL from a young age if they can handle it because the good ones tend to do things that make them valuable NHLers from a young age. Speed and skill, even and small doses can fill the margins for a team looking to get an edge on the competition. Even if young players make more mistakes, the return on those players development in the long run for their organization, probably pays off. This is not to say that players should not play four years in junior; it is only to say that instead of keeping players in the NHL forever, they should be challenged in the NHL sooner, allowing them to be tested while playing at the highest level.
With older players scaffolding can lead to constant evolution and growth, even if a player is thought to have stagnated. If the player is willing to learn, there is no reason to pigeon-hole them as a certain type of player. Skilled players can develop defensive skills or become penalty killers. It can allow them to play more minutes which should help the team win more if the team is properly constructed around them. Pushing players just a little bit to evolve can push a team over the top. That should be reason enough for a team to experiment with the idea of getting players into the NHL quicker and forcing players to learn on the job, whether they are a rookie of a veteran.