GROVER wrote:
A clerk at my local Ace Hardware told me to use Teflon tape on the
pipe threads but not the compression fittings. I'm trying to stop a
very slow seepage from the couplings and flex hose surrounding a
quarter turn shut off valve serving the cold water faucet to a
bathroom sink.

Is this advice correct?

The purpose of Teflon tape is to lubricate the threads so the fittings go
together more easily. Teflon tape is not designed to be a sealant, even
though it may act minimally in this capacity.