Anti-seize typically contains fine metal particles (copper or zinc) that serve as a sacrificial anode. This prevents galvanic welding of dissimilar metals (eg. Al and Steel). Heat + water vapor (like you get at the interface between a spark plug and cylinder head) is one example where this occurs. Liquid water + salt (from sweat) dripping down the seatpost is another. Anti-seize is definitely not overkill for bicycle applications. It's a little more expensive than plain grease, but a little goes a LONG way (I'm about half way through the tube of Permatex anti-seize I bought in the late '90s) and it can significantly extend the maintenance interval where it is used.