I think this is a very interesting point and something I clearly pointed out and proved to one of my fellow musicians only recently.
Here's my story: We played a venue recently that we knew had a very sensitive sound limiter. A 3 second threshold and all power off. Yes, one of those We knew it was going to be a tough gig so our usually sensitive drummer even brought an electric kit instead of his usual acoustic kit. I mean sensitive in that he's every bit a professional drummer who knows what kit to bring to what gig and knows it doesn't need leathering for a great sound. Anyway, I digress. The discussion was that as the limiter is set really low we should only take the 12" tops for the PA because the subs would be way too much. (The venue was actually very large). My response was actually no, we'll take both subs. We will go with the fuller sound even if we DID have to play relatively quietly. As it happens, the limiter was so badly configured that I managed to take a selfie video with me talking, right up against the PA speaker which was playing music at a volume just under the limiter's threshold. (yeah, I know, geeky, but we did test both the threshold and the resonant frequency band of the limiter.)
Now, you may be asking, what the actually flibbertyjibbit has this got to do with backline? - It's a common misconception that a sub is always all about booming low end, like some teenager's vauxhall nova with a huge bass speaker slapped in the boot. If your system is set up properly, then you should be able to experience support in the low end that a well selected sub brings. Looking for a description, I'd say 'flat response' all the way down, rather than the hyped pumping lows of say dance music. Let's say 'girth' to your notes rather than attempting to blow your audience towards the back wall. A good option when you have no PA support as an example.