Interesting (by the way, that wasn't supposed to be a flippant or sarcastic post, though in retrospect it probably read that way).
I got my PPL under a different regime (australia); I've always used everything on every takeoff calculation - headwind, tailwind, surface (short grass hard base / long grass, soft base). As standard a certain amount of margin is mandated to be built into the POH, which I wouldn't touch - POH figures all the way.
Then having arrived at a final number, my personal practice was/is to make a judgement call on how close to that number I'm willing to go, based on a whole bunch of factors: currency and familiarity, confidence in the numbers, stability of any headwind, predictability of the surface (grass in particular being a very variable animal - encompassing anything from almost as good as concrete to absolute treacle - how a single grass factor can be published I don't know!)
I'm no sky god, but personally I'd rather know what the theory says, then fudge some safety onto that, than use a very conservative estimation tool that gives a factored number - and make a go-no-go on that number; My thinking is that at least I have a feel and awareness for how hard I might be pushing it vs the other system where I'm not making the call. Of course, if you get down to making decisions based on single digits it's probably time to take a long hard look!