I agree with the waiver wire "conservatives." Common sense dictates that it almost never makes sense to reduce your cap size relative to other teams with two exceptions, one already mentioned above --
Dumping your scrubs at the start of the season and using the extra $1.4-$1.6 million in cap room to pick up another reliever or upgrade a position player. That's a no-brainer. Though you pay a 10% tax on the $1.4-$1.6 million, it's still found money.
Realizing you have a better-than-expected AAA player and using him to replace the position player you drafted. That's a little trickier because you need to have TWO better-than-expected AAA's, since one won't have enough PA's, or you have to pick up a low PA player from the WW to pair with your AAA player to stay above the minimum PA requirement. Sometimes that works and sometimes it blows up in your face.
When owners go to the waiver wire in other scenarios and miraculously "reinvigorate" their teams, it usually means that their team is benefiting from a statistical change in fortunes that would have happened anyway and they got lucky and weren't penalized for reducing their payroll.
But the bottom line is that going to the waiver wire on a regular basis is a recipe for disaster unless you're in a high cap theme league that allows you to pick your own WAA AAA's. My 0.02...