I don't mind teams playing their first round pick if the only option they have is to send them back to juniors where they've already proven they're way ahead of the competition. For example, Mitch Marner will start the season with the Leafs next season since he's too young to play for the Marlies (he'd need to be at least 20) and he's already conquered the OHL and sending him back for another season would only slow down his progress.
First year picks rarely make the big team. But it happens and they usually already have the skill set and maturity to compete and stay with the big team. Usually, those players are among the first 5 players picked. This season, Noah Hannifin spent the entire year with the Carolina Hurricanes. He was among the top 3 players chosen. Marner could have started the season with the Leafs, but Toronto announced to the world that they were going to be on a full rebuild from the start of the season for the next few years to come. No use wasting Marner when he can spend the time improving on his already considerable skills and getting stronger with one more of junior under the Hunter brothers. What i'm guess will happen this coming season is that he'll start the season with the big team and wind up spending a lot of time in the press box. They'll then be able to manipulate the rules by sending him to the Marlies on a conditioning stint, and once that stint will be done, they'll loan him to the Canadian junior team for the world juniors. And once the juniors are done, he'll be sent back to the Leafs to complete the rest of the season.
At this year's draft, the top three picks are expected to make the big team. I'm actually 100% certain of this. They are ready to step into the NHL. The fourth and fifth picks (whomever they are) could surprise a few people and make the big team, but i'd personally be surprised.
Another reason why it's not a bad idea to send back a pick to his junior team is that the team maintains at least a year of control over the player's future contractual situation. That's why i've always believed that Galchenyuk should have been sent back to the Sarnia Sting after he got drafted. He could have developed more and be more ready to play in the NHL, and the habs would have got him for cheaper longer. Watch out when he signs his next contract!! (which is partly why i believe PK Subban will be traded prior to July 1st.....the habs will need money when they have to re-sign Price, Pacioretty and Galchenyuk in the not-to-distant future).