50hz is an odd number to me, but there's no set in stone answer. I've been told 31hz, 40hz, 70hz, 78hz, and 80hz, even 100hz, but never 50hz. Again, no set in stone answer. I'm lucky enough to have a monitoring chain and references I can trust(a few sets of speakers, headphones, car stereo, ect.). I CUT WHAT'S CALLED FOR TO SOUND GOOD IF AND WHEN NEEDED AT ALL.
Cutting lows usually give your bottom end a "cleaner"(for lack of a better word) signal. Even though it does take out some of the thickness in your lows, when done right, it should make them sound waaaaaay better. Keep in mind(I'm not gonna pretend to be an expert, I trust my ears more than numbers)most speakers won't even play back signals below 40hz(or somewhere around there)without distortion and noise. Same for highs, the whole point of cutting and shelving freq's is to make them compatable(for lack of a better word)with everyone's listening devices.
Think of it like you have a huge painting that you can see in it's entirety, but you sell it to someone who's wall is smaller than the painting. You wanna cut off the edges just right so they still get your full vision even though the picture is gonna end up smaller. Hope that analogy didn't confuse you. Hopefully someone else can give a clearer explanation. I'm sure mine sounds spaced out as hell, lol.
Best way to understand freq's is experimenting with the finished product. Cut your lows at a few different freq's between 31hz and 120hz throw them all on a CD and just play them in multiple systems, make sure you test in a car. It'll start to make sense.
Definitely super duper late in this threads life to be adding a post but deRaNged I want to commend you on your answer and add a bit to it.
As always, i'll preface this whole thing with "every tracks going to have its own unique EQing depending on the sound your going for, it's up to your ear, don't pigeon hole yourself, etc etc". I think this is very true, and I think really just keeping an open mind. Keeping your approach simple, whatever it is, is key when it comes to experimenting. Just like in a science experiment, you only change one variable at a time and you count and keep track of
everything.
Now having said that, I feel like music and its creation has a duality with deh "Science" I ramble about. More specifically mixing, which is ultimately what this thread is about. There are definitely guidelines, "pseudo"-rules, tips and tricks when it comes to mixing. Some of these you can apply in more or less every track; general EQing, compressing the whole drum kit (depending on type of music to a degree), leaving 3dB - 6dB headroom when your done.
Bringing it back to the thread topic and your question...I cut most of my kick drums and bass/sub channels with the Auto Filter (Ableton 9) @ exactly 50 Hz w/ the Q set at .81. The Auto Filter, even with the cutoff @ 50 Hz, is still letting some of the lower freq's pass through. I think the difference in sound and general lower clarity is indispensable
for the style of music I make.
Generally speaking, every frequency present in your overall mix is taking up space in it including ones you don't hear. This results in less headroom and reduced dynamic range, esp in the freq regions closest to the offending ones. And like Deranged said, not a lot of systems can even accurately play back frequencies up 50 Hz. Our ears can't tell a pitch from it either, its really only meant to be "felt" (I think, anyway). I make East-West style hip-hop typically, and my main focus is thick kicks over meaty sub or layered basses.
At the end of the day it comes down to preference, as has been said a billion times lol. I think adding that 50 Hz HPF compliments my style and the other material and techniques I've picked up. Everyone eventually accumulates sounds, FX, techniques, tips and such that they use over and over. It's our style and brand, and is hopefully memorable or unique enough to strongly stand out while still sounding good.
Hows that for a space out answer haha. Enjoy!
yet i'm wondering if there are some sounds that need to keep freqs below 50hz such as bass ? 
