I may have a max bid in mind but ideally I'd still get it as cheaply as possible and well below the max I would actually pay. Hence leaving it as late as possible to enter it.
Problem with putting a big max bid in is sometimes it can be driven up on purpose. Whenever I've done it in the past, if I did win, it went all the way to the max. I rarely use eBay anymore except if I can find it cheaper with BIN than anywhere else.