[CQ-Contest] Optical and galvanic isolation

[Paul Young]

I'm building a keyer and headphone switch box for my small contest
station.  I have a few questions:

Some keyers use optoisolators for the key and PTT lines and others
just transistors or FETs such as the 2N7000.  Has anyone had an
experience where the optoisolator actually helped or saved equipment?

Some headphone switches use transformers for galvanic isolation.  Has
this solved problems for anyone?  And can anyone recommend a source
for a good transformer for this purpose?

I understand that isolation and transformers "good things".  But if I
put all good things in this box it might not fit in my small contest
station.

                              Paul, K1XM