"M" wrote
Is it standard procedure to install them and leave them in, or is it
desirable to remove them when the additional height is not needed ?

You just install it once, and leave it in.

About the saws I am looking at - 14" multi speed capable, enclosed motor
I have narrowed it down to two, with the essential differences that I know
of so far

Delta 28-206 2 speed 16" table, , fast tension release
King KC-1433fx 3 speed, 15" table,

I can't comment on those saws specifically, but my saw has a tension
release lever which is _extremly_ handy.