Setup is about being fast enough. Hold is about not being too fast. Fix one and you'll often break the other.
The Trade-off
Inserting buffers to delay a fast path adds area, power, and — on adjacent paths — setup pressure. The art is local fixes that don't ripple.
Useful Skew
Intentionally delaying clock to the capture FF gives you setup margin AND removes the hold issue. PrimeTime's useful-skew engine can do this automatically.
ECO Loop
Always: fix → STA → check setup → iterate. Never blanket-insert buffers without simulation.