I can't guarantee anything. But players I list on June 30th always seem to get an offer during the transfer period, even though sometimes that offer doesn't come until Deadline Day two months later. If I wait until July 1st, I might sell/loan them, I might not. I have been much more successful since I started listing them before transfer season.
The biggest downside is that sometimes I can't be sure who I'll be able to sign, especially since I always start careers with low budget teams. A couple of times I've gotten stuck after selling a decent player at a particular position but missing out on signing the player or players I had targeted.