I can't say how important it is in '20 (haven't played it yet) but I've found in the past that building up your AHL team really helps. For one, a strong team can go deep in the AHL playoffs, giving your prospects more playing time.
For prospect forwards I put them on a line with two strong (rating-wise), complimentary veteran linemates. E.g. if the prospect is a sniper, pair him with a solid playmaking center. Players in the mid-to-high 70s are easy to find as free agents as there are dozens and they're all cheap contracts. The prospect should also put up solid numbers with a strong team around him, as long as you don't put him too far ahead of his comfort level (say, a 62 overall shouldn't be on the top line).
For d-men, same philosophy.
If I have any eligible prospects on my NHL roster, and assuming the NHL team misses the playoffs or is eliminated early, I send them down to AHL for their playoffs. Again, more playing time and possibly help win the AHL cup.