Reply to Mono Producing

What are the benefits of mono mixing, or producing? Whenever I switch to my master channel to mono to see how it sounds and to mix the volume levels, sound and actual volume of the instruments changing way too much. Can anyone explain the mono-stereo difference in producing.

I didn't do anything special about it since I was reading about mono producing for kicks and basslines(things below 300hz) and club PA systems being mono etc, now all the previous informations are colliding with this new information I just happen to read.

I will be happy if someone explains it in a different way or better ?