Tbh I haven't been keeping up with the times on chaff so it would appear - didn't know it is synthable now. I try to avoid chaff as a crutch, simply because I have no real need for it in PvE and in PvP I build to beat largely fixed opponents. A lot of high-skill players use fixed and if ya outfit to beat the best, you'll beat the rest anyway. Of course, that doesn't mean I actually beat the best
As you say it's all about a bit of common sense. I don't bother with PD on my iCutter, but I'll regularly use a single one on my FGS, which is a hybrid tank and can lose a lot of its firepower to a missile in the face.
Iirc OP is flying a Viper mk. IV at present, which kinda does benefit from the PD. It's small enough that one or two missiles will really hurt it, but doesn't have mega speed to control distance from the missiles when you know they're incoming - and a CZ is often too busy to keep a tab on what your opponents are all using.