<p>I've found many Youtube videos of makers upgrading to BLTouch sensor. </p>

<p>I have a Creality CR-10S Pro, so far bed leveling hasn't been an issue (after some days of trial and error). </p>

<p>My question is what are the problems/issues users need to face in order to need (or justify) an upgrade?</p>

I don't know your printer but I don't have BLtouch, and I have to set the height every time because the bed expands with heat.
If you print at variable bed temperature (PLA, ABS, PETg, nylon require different values) then that sensor helps a lot.
BL touch can also speed up bed calibration: you scan the bed, see the values to be corrected, adjust the bed without having to guess (given the thread pitch and required correction).
Also, if you print only in the center it's easy but if you print fully using the size of the bed, I doubt you can get very flat bed. The BLtouch helps for that too.
Also, there are clones like 3D touch which were tested and work equally well. Depending on your budget, they may be an interesting alternative.