The thing is, a standard guitar is designed to be tuned EADGBE and fitted with a set of strings that all feel more or less the same tension when tuned to standard tuning. Even then, a guitar needs to be set up correctly to play more or less in tune and there is still a good chance that some notes, in some places, will still be out of tune sometimes (but with luck no one will notice).
Trying to change the tuning of any instrument with strings (piano, violin, mandolin, guitar etc.) will potentially cause tuning problems. With most guitars tuning some or all of the strings up or down maybe a tone shouldn't cause problems that can't be solved, but anything more than that will almost certainly cause issues that can't really be fixed.
I don't know for certain what you mean by "drop B" or "drop A". To some people this would simply mean, B (or A) A D G B E. I'm guessing though that you don't mean this and that what you want to do is to de-tune the whole guitar and end up with something like A E A D G B - sorry if I got the maths wrong but listing the actual tuning would have been helpful.
Now, a set of strings starting with a 0.012" or a 0.011" are just standard gauge strings - the same gauges people still use on acoustic and the gauges we all used to use on electric. I really can't see how you could even tune them that low and not have them too loose to play.
If you were happy with those gauges or (especially) if you used heavier strings then, as the Dawson's employer said, you will have intonation problems. The thicker the string, the longer it needs to be - that's why a guitar with steel strings has its bridge slanted. It's very unlikely that you will be able to adjust the bridge saddles far enough back to have the guitar in tune. Add to that, that the strings are either too thick or too loose for a standard guitar then your tuning and playing problems are made worse. Also remember that if you use especially thick string you're going to need the slots in the nut widened and... well rather you than me.
I wouldn't want to say that what you suggest is actually impossible but I agree completely with the advice you were given. I always say that if a person doesn't like the tuning of a guitar they should get a baritone guitar (or a 7 string).
Yes, maybe you have seen people doing what you suggest but I'd say they are either playing guitars that have been altered in some way or they either don't notice or don't care about the intonation and playing issues.
There are many things that are possible but not really workable. I remember decades ago needing a bass but not having one. I de tuned the bottom three strings om my acoustic (which was fitted with a pickup) and used that. I still have a recording and no one would know, they'd just thing it was a badly tuned bass played badly.
Added, just to put what you are suggesting into perspective, the low A string in your drop A tuning is going to be a whole octave below the "normal" (5th) A string on a guitar. Take a look at the A string on a bass and consider that the scale length of a guitar is a lot shorter than the scale length of a bass so you'd need to have a string even thicker. If it's not then it will be too loose to play. If it is then there is no possibility of being able to intonate it correctly with a standard bridge.