Well, it's better than keeping your foot on the brake and dazzling the
driver behind you which is what a lot of people do! AFAIK you should keep
your foot off the clutch at all times except when changing gear.

It is completely wrong IMO.  When stopped you should apply handbrake and
select neutral.

Takes the gearbox load off the engine - but it's no benefit whatsoever
for a running engine and gearbox in good order.

Correct! You'll prematurely wear out part of the clutch doing so. Do
as Catman says except for a short wait (say less than 15 seconds?)
don't bother with the handbrake.

It's not good practice.

It will wear out your release bearing faster than is necessary and if you
have the footbrake pressed as well, you will dazzle drivers behind, as well
as warping your brake discs with your hot pads.