Eh hem!...Subwoofers... What do ya know?

Subwoofers are a thing.  A thing to love.  A thing to avoid.  A misunderstood thing.  

What are your opinions on subwoofers?  What did you learn and how did you learn it? 

128x128jbhiller puzzles me why individuals buy speakers with poor bass response...

Bah ! Subwoofers ! You kids and your rock and roll music . 
My mains have all the bass response I’m sure some would like to have . But i also want six subs . And since i do what i want ..
seriously though i think people do not use them properly to get a hifi effect out of them . I guarantee the majority could turn them down a notch to achieve proper reinforcement. Turn it down to the point where you actually have to feel the woofer to see its on . Then leave it there chances are if its in the right location as explained ten times on here it will sound perfect . 
Regardless of your main speaker capability in the bass, there will be instances where you will need bass re-enforcement in the room. This is going to be dependent on the room size and acoustics. The alternative is also true ( but far less often). For example, I know of a fellow a'phile who uses large Wilson Alex 2 speakers in a relatively small room. The Alex 2's have large bass drivers and can drop down into the lower 20Hz range. This fellow tried to integrate subs into his room, with little success. The reason...simple! Because the main speakers were large enough to fill his room with accurate ( this is the key point here) bass! In this particular case, it was obvious ( well to most experienced a'philes who listened to this system) that adding additional bass that essentially overloaded the room was actually undesirable! OTOH, in most other cases with speakers that can go into the low to mid 20Hz's with some ease, adding a subwoofer of commensurate quality ( Yes, that is also a very very important factor) will allow for a more defined stage and more accurate ambience retrieval.
 I recently attended a demo of the new ( and superb) YG subwoofer. In the VERY large room that this was demoed, it was quite obvious that the subwoofer was a major addition to the overall SQ. The main speakers were well equipped to drop down to 25-30Hz...YG Sonja's...but add the subwoofer and the whole became a lot more than the parts. Something that is quite obvious once you experience it...and perhaps less so if you are just theorizing! 
@davekayc I'm fighting a bass null at the sitting position so I wondered about, having the mains spread further apart but toed in at a steeper angle to limit low frequency waves going straight at the wall and being reflected back. Basically having the very toed on speakers sending low frequency waves at the rear wall at a steep angle vs nearly head on to negate the null.

Unless I move at least 38% of the way into the room (better at 50%) I sit in a mid bass null. I always thought the speakers were bass shy but the sub I've been messing with has the same issue so its clearly the room and not speakers. If I mive 3ft to the right of the couch/sitting position which puts me in front of the hallway entrance the sub is delivering THUNDER. Move back to the sitting position and its a little warmer at best.

Right. Same here. Same everywhere. Exact same situation in my room. 

The solution is, first move the main pair and seating position around listening for smooth but not necessarily deep bass. Just try and avoid the worst spot, basically. The bass we will fix later. Then at this point get very precise in tweaking placement for imaging. It is essential at this step to get the speakers exactly equidistant and toed in perfectly symmetrically. Finally, add four subs, one on each wall, wherever they can go but preferably no two the same distance from a corner.

What you will find, any single sub or speaker does exactly what you heard- lumpy uneven bass. Moving around only moves the lumps around. Adding more however creates lots of lumps that all together average out to really smooth. The wavelengths are so long and we hear bass so much differently that it hardly matters where they are, but it does matter a lot how many there are. So use more and the problem solves itself.