If the limit is TOTALLY abolished (instead of being changed to 40 or left at 35) then there is a possibility things COULD get out of hand.

In one league last year I got Tony Phillips basically as a throw in in a bigger deal and in another trade I got Bobby Bonilla as a throw in. Now you may think this sounds pretty harmless but Phillips had an OPS of about .950 against lefties in 1998 and Bonilla was eligible at 3B and LF and had a vs. LHP OPS of around .820 (if I remember correctly).

Towards the end of the trading season I also got a couple relief pitchers (which were borderline keepers for this year but useful for last year) as throw ins in other deals although it wasn't specifically stated that way.

If the roster size HAS NO LIMIT then every time you do a deal with a team that is out of the race you could ask for a player that is worthless for the following year as a "throw in." Do this enough times and you could accumulate a nice arsenal of players for your active roster.... while still being able to keep as many younsters as you want. In other words you could draft a bare minimum roster of useful players for the current season and then have maybe 10-15 prospects, knowing that you can get the part time fill in players as "throw ins" in other deals.

With a 40 man roster we could at least keep things semi-realistic. I don't think its realistic for a team to be able to accumulate 35 players that are useful for the current year and also stockpile 15 players for the future (with no current value). At some point you have to make a decision whether you would rather have Ryan Christiansen for now or Roosevelt Brown for the future.