Well, if I see a player similar to the 89% DC as described above but at say at 78% in the first week of next season, then it is better to get him as he will be 1 year younger but close to same quality as the 89% DC will gain some % during his short time at the club but will lose 20%, but what if such a player do not show up at all in the 1st week or 1-2 show but with relatively high bids on them at the near end of the auction? It is not like old times where only a small amount of users knew about fast trainers and so on, and that there are only 2--3 different levels that can bid for the same players. In other words, competition has significantly increased for even a player in 75-85% range, and there is no guarantee the player will appear in this range itself.
One advantage of having bought the player the previous season is you had opportunities to test him before investing in him but then there is no guarantee he will perform same or better next season. A disadvantage is the significant loss in % quality relative to the level being played which will have to be compensated.