Why would we need it here? I don't think there's ever been a single discussion with a spoiler for anything.
I suspect that what he's asking for isn't (the semantic meaning of) a "spoiler" tag, but rather the functionally equivalent (but with different semantic implications) "readmore". In other words, a way to include a large amount of text in a post - say, a thousand lines of source code - which is only shown to people who are actively interested in seeing it rather than forcing everyone to scroll past it.
In theory, I think that's a great idea for just about any site, but especially for sites dealing with programming or where very detailed discussions tend to take place, since they tend to generate longer posts. In practice, I don't place a high value on it because the people who should use "readmore" tags rarely do.
