Very, Very rare:
I would stay up (all night if necessary!), set AS to $102.78 and just in case AS is running slow, place a manual bid for say $87.78 as late as you can in the auction. With manual bids that could mean 20 seconds before the auction ends! This is only if it is so rare you have never seen another one. I have only done this twice in the last three years. "Belt and braces" where I must not lose!
Rare:
Rely entirely on AS, but have a bid loaded and ready to go, if at the last minute, the price igoes higher than your pre-loaded AS bid, because you underestimated the market price, but still must have it even if it means exceeding your original limit.
Moderately Rare:
Rely entirely on the bid you put into AS in the first place. If you lose it you will find another one, perhaps with difficulty. If the market wants to give more than you - let it!
These are my three sort of value judgements based on my experience. Other snipers here may disagree, but you did ask me to explain my actions.
As R2 frequently says, there is always another one round the corner.
Paul
P.s. Always exceed obvious "benchmarks" $100 bid $103.78 You will find that most people bid $1 or $2 at the most over benchmarks like $59, $100. So just take it a bit higher and always
bid between .55 cts and 95cts in an auction that looks like it is going to be faught over.