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.