The reason people do it is this

If you have for example 20M in the bank and you see 2,3 or 4 players on the transfer market you want at 20M each. If you have the tokens you can bid on all of them and then if you win them all sell off who ever you need to to get you bank balance back in credit.

In the early levels i did it ever year and found it a great way to upgrade your even if at the time i was a little cash strapped. Thankfully i never got to the point where i lost players.