What is wrong with a sub?

Using my brain, not my ears, seems that the lower freq are just fine located in different locations.  I would not buy a full range speaker until I had this figured out.  If the speaker is just more cone speakers of different size and the bottom one is big - why not have it located someplace else?
 
In live music the instruments are in different spots.  Bi-symmetrical (stereo) may be because we are bi-symmetrical with two ears.  However lows are both felt and heard.  I feel a sub which is why for me speakers sound better than headphones.  I'd rather move the sub around. 

Never had much success integrating a sub in a 2 channel system.
Always found it reduced upper frequencies transparency even when set up right.

Guess the benefit of being old and new (to audiofile stuff ) is I have not had that issue, which was the reason behind the OP.

Integration not always easy

Stand mounts with subs are regularly suggested to me as I obsess over my next pair. But apartment living seems like subs would be a no-no. I had been looking at stand mounts that hit around 40hz so I wouldn’t need a sub, but I’m discovering that even with my current (rolls off at 50hz) parts of the room load up and I feel like that’s where I’ll have issues.

im coming around to integrating a sub, but afraid my situation won’t be a workable one. I may just buy a refurbed or scratch and dent sub and try it and see how it goes.