Sorry Yogiboy but as you see from the good advice offered so far, there are not just a few simple answers.
But I might suggest answers start with how many mono records you own (i.e. how much time will you spend listening to mono?) and how anal you are about LP playback? Then consider:
Is it a true mono design cartridge (see above) or internally strapped for mono (some claim this for Grados but I don't know)?
What size and shape stylus do you choose?
Are your mono LPs original (larger, conical stylus could be better) or recent reissues (mono cutter heads no longer available so reissues are cut with stereo heads, thus modern stylus tip could be best)?
Does your arm offer easily adjusted VTA (older LPs cut at different angle, see Fremer's article in recent Stereophile)?
If your mono LPs are originals, you may want to consider alternate EQ adjustments. Although the RIAA curve was approved in the mid-50s, some labels continued using other EQ into the '60s.
Back to the original question, a mono switch on your phono/pre should allow for quieter playback, thus more enjoyment. But there are many steps beyond and only you can decide how far to take it.