When was the last time :
1) You did a w&b calc
2) You saw anybody do a w&b calc
3) You heard a FI say "as long as it's up to the tabs it's fine"
1) the last time I was PIC
2) the last time I was PIC
3) Never, my FI taught me W&B before I went solo and expected me to confirm that (a) the ac was in limits and (b) whether it was normal or utility before each sortie
I have always flown aircraft (mainly PA28, but also C15x/172/PA32/B121) which were capable of getting outside limits quite easily.
And I don't think that legal is necessarily safe either - I once rejected a take off in a PA28-140 due to unexpectedly poor acceleration, when I KNEW that we were 50 odd lbs under gross. I still feel good about that decision.
If the authorities believe that 10% overweight is safe, why is it not safe? Still waiting for the answer.
They don't for normal operations, so it isn't for normal operations.