Thermal insulating pads: Replace every time, or re-use?

[cvanc]

I've always replaced them, even when they looked fine, but I wonder if I'm being more conservative than I need to be?  Is it really necessary to replace these every time?

What do you do?  Thanks.

[TERRA Operative]

Depends on how lazy I'm feeling and how critical the part is.

Vreg for a relatively low power PSU? usually reuse if it isn't too old. Expensive ASIC or FPGA or other esoteric or critical part? New pads all the way.

Sometimes I'll add a tiny bit of thermal paste to each side of the sil-pad too, it helps stick things in place while I fumble around with the mounting screws etc.