Lowcountry Low Roller
My thoughts exactly. This is not necessarily about having a radar to identify a threat in the distance, but for determining surprise when the balloon goes up. Does your "spidey-sense" tingle or not? And a perceptive PC can certainly pick up clues related to the looming threat. But they're not going to say "30ft over there are two dire wolves lurking waiting to ambush us, so let's nuke 'em and move on. Yawn..."It could also be argued, at least in the case of Stealth, that surprise is a very powerful effect and that even monsters one imagines are good at lurking can't pull off surprise with certainty or near certainty all the time. Even so, a monster with training in Stealth is likely to be able to surprise some of the PCs but not all and that's still pretty useful.