What is the norm? How many of you use the subsonic filter with your turntable?

I agree with others about using rumble filters. If there isn’t a problem with warps or bad mastering, woofer pumping is a sign of setup issues. In that case a rumble filter is a band-aide that does nothing but – maybe – mask the problem.

In many cases using effective isolation for the turntable can resolve issues.

Years ago I had a tonearm with magnetic bearings that caused woofer pumping. It was the wrong arm to use in my environment. Once I changed it to a gimbal tonearm with mechanical bearings the issue with woofer pumping disappeared instantly and completely.

I now use a HRS rack and isolation base for my turntable. Nothing upsets the table now.

sometimes. 

I also have a Hegel V10 phono preamp and don't use the subsonic filter.  My SOTA turntable (with vacuum holddown platter) sits on a special heavy shelf in my Target stand, so there's no need for a subsonic filter.

I use a subsonic filter, -3dB at 8 Hz., 24dB/octave. I use it when I listen at loud volumes. It can be switched in or out through a tape monitor type circuit.

I do not use one or needed one. Haven't had that problem in about 40 years. As the quality of my turntable went up. Typically it is a resonance problem with your turntable or compliance mismatch between tone arm and cartridge. Perhaps there are some other possibilities. But look at your turntable and setup to find the problem.