Well, what if you make a 150,000 G bid (this is the minimum) on the best available player (based on your needs) within your budget, and then a preferable player (maybe younger and/or with better stats where you want them) comes on the market a day or two before the deadline for the first player, but now you can't even make a bid because your money is tied up. You check and see that your bid is the only one made on the original player. Wouldn't it be nice to retract your original bid so you can go after the alternative? Even in the pros, if you don't get a response to your bid in a reasonable amount of time you can retract it.
Also, what is the point of having to maintain at least the minimum bid on a player for which you don't even have enough funds to match the average bid? The current system entices users to wait until very late in the bid process to make bids on players with high minimum bids. Finally, because bids are accepted around the clock, it may be very difficult, if not impossible, for someone on the opposite side of the planet to do this. What if the server is slow or is timing out!? The emphasis on last-minute bidding should be curbed, above all else, IMHO.
I disagree with gabrielis that the max bid should be displayed because it would decrease the realism associated with bidding on players. In TRW, clubs simply don't know what bids other teams may or may not have bid; they don't even know the minimum acceptable bid, let alone the average of all bids.
Maybe a better option than the ability to retract bids would be this:
Minimum and average bids are not displayed, but the "get expected max bid" option remains. If you make a bid lower than the average bid (or your accepted bid falls below the average), then it gets rejected, but not immediately. Instead a notice that "your bid was rejected" shows up in your club news a few hours later, or half of the remaining time for the last few hours. Only once you make a bid that is accepted (i.e. above the average) can it no longer be changed downward. To prevent anyone from accidentally entering an extra digit, a confirmation notice would pop up after you enter your bid asking "are you sure you want to enter a XXXXXXX G bid?" that is only entered once you confirm it. Bids over 1 million should have to confirm a second time. This would encourage users to start making bids earlier (starting low and working up) thereby decreasing the "time zone effects" I mentioned earlier, while also increasing the realism of the bidding process. It will also discourage teams with limited budgets from getting in over their head, so to speak.