I think we have a winner! Why on earth would you ever need to use that SEXP? Even in mission testing it would be far more sensible to put a message in its place saying ERROR. 
I`ve found uses for never-warp and allow warp. They are very useful in missions where you want the player to make use of a jump node. You could probably base a mission around a broken jump drive and thereby make use of break-warp so it isn`t completely useless.
I agree with you about ship-guardian what's the point in a SEXP that prevents weapons from doing damage but stil lets you get blown up by explosions and the like.
I haven`t bothered with the others you mentioned so I guess they really are useless
Yeah, on second thought those warps might come in handy if the support ships can repair jump drives with one set of operators but not the other.
The other two actually crash the game when you try to use them (Volition didn't implement them properly), so they are pretty much useless.
I think debug rises high above them all though, since it is
supposed to crash the game with an error message. I can just dream on about of all the possible uses of that.
:D They went as far as to give debug its very own category as well. (it should be renamed to "pointless sexps" or something like that)
