The background

Your bid is a binding contract

One reason not to bid early is that eBay considers your bid a binding contract. While it's technically possible to retract a bid, eBay frowns on that. You can get in trouble if you retract a bid without a really good excuse, like accidentally entering a bid for $1000.00 when you meant $100.00. If you retract bids very often, any excuse you use will wear thin.

It's best to decide on your maximum bid early in the auction, then "sleep on it" until near the end. Until you bid you are free to change your mind any number of times.