Resonator banks. I don’t know why, but having to re-tune my instrument just sounds like a fundamental flaw that I should have discussed with myself long before I pulled out a resonator bank. There are probably some great uses for it, but I haven’t found any on a personal level yet.
Flanger. Yeah, maybe if I’m trying to do some shitty classic rock solo. But I’ve never used it.
Phaser. As everyone else seems to agree, see flanger. Cool for guitar, if you’re 50+
Looper. Live has one of these and it seems redundant because the whole DAW is a god damn looper. I’m not Bruce Willis, and neither are you.
I’m sure there are more, but adding in loads of these that don’t apply to me because I don’t ‘jam’ or play live would get monotonous.