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

First, if you carefully match your cartridge's mass and compliance to that of your tonearm you should be able to achieve an optimum vertical and horizontal resonance of between 8 and 12Hz. This is precisely what you do to ameliorate the effects of record warp information being amplified and sent to your speakers.

@dman777 @faustuss ^^ This!!

My preamp has bandwidth to 4Hz. I've no problem with excess woofer excursion at all.

I use Sota's Reflex record clamp.   It's a nice accessory 

One must also consider the resonant frequency of the cartridge/arm setup. The goal here is to place that resonance between 7 and 10 Hz. 

This resonance causes an increase in noise (separate from the system noise) that peaks at the resonant frequency. that peak can be quite broad or it can be narrow, depending on damping. 

In my system, that peak occurs at about 50dB below the signal (1KHz test signal). My system can reproduce frequencies down to about 5Hz. This frequency band is not audible and may not cause woofer pumping, but it does use up some power in the amp and preceding components. The KAB RF-1 that I use cuts this peak by about 30dB, very significant. The loss at 20Hz is about 2dB.

This is another factor to considering whether to use an ultrasonic filter or not. I use on as I find it very effective at significantly reducing resonance noise as well as rumble.

@dman777 

I had a Lehmann Black Cube SEii phono stage that came with an adjustable set of bass roll off filters  

With a tube amp and subwoofers the filters did help make the sub bass and mid bass faster and with better snap / punch.  

A tube amp may be an area where subsonic filters are most useful by avoiding wasting precious tube amp power.  

A tube amp may be an area where subsonic filters are most useful by avoiding wasting precious tube amp power.  

@avanti1960 Having run tube amps for decades, I can tell you this statement isn't correct. What is important is getting the tone arm and cartridge set up properly so the mechanical resonance is in the right window as described by @kevemaher . If that is done correctly then there's no need for a filter regardless of the amplifier.