Auto bid is set max amount. Then the computer will help bid for you
Let's say the player price is now $1000 with 1 bid, you set $10000 as auto bid, then the computer will automatically bid the lowest amount possible until it hits your autobid amount.
So let's say I bid $5000, minimum increase is $1000 or 10% right? So since it's still below $10000, the computer will bid $6000 for you. If the auction end with no one bidding more, then you will buy the player at $6000 (instead of the $10000 max you put). But if I bid 9500, minimum bid will be 10500 at least, but since it is above your autobid amount, so the system won't bid for you anymore.
In short, last time if you want a player at midnight and don't want to wake up to bid, you have to put a high amount, then pay that amount. But with autobid, you still can put that high amount, but if no one bid, you will pay less than what you put in.