It depends on the bike. Honda and some BMWs has linked brakes so you do not have too much option there when you use front it presses to some extent the rear brake too. Some old two stroke drum brakes the front was pathetic and dangerous.
On the Fazer I use rear for filtering a lot, in the wet or muddy, mid corner sometimes. Probably will use it on snow. Bear in mind I like soft organic pads rear, which makes it very gradual and when I say use I mean very soft gentle nudge too. Even in filtering my "aggresive" rear use is probably never more than 40% of its full capacity before it locks. When you are in the middle of the road on the chevrons where there is plenty of white paint, road debries and whatnot you have to be very gentle on the brakes
Normal slow down I use front to shave off most of the speed, than final stop on lights I finish with rear touch that is just to put my left foot down and leave my right foot on the rear brake and pull the clutch. I am in 1st so when its green I just get up my left foot, get off the clutch and get on my way.
When I need to slow down fast I use front only. The Fazer has so good brakes that I always use two fingers only for the front. Even in emergency so far. In such case can't use rear anyway because when fast my feet balls are on the pegs away from the rear brake.