I don't know what the consensus is on here, but quite frankly, I MUCH prefer to check myself for dilation than someone else. I know my body better (especially after "knowing" my cervix while tracking cycles for the last 9 years) so I can gauge changes better, my body already knows my own bacteria, I can FEEL (inside, as well as by touch) what I am doing, instead of someone else just feeling with their fingers, etc.
I don't think that just because you know what you're doing that you will be doing it too frequently, but at least if you feel the need you will be familiar with what you are looking for. (and really, "frequently" isn't something I'd really be concerned about as long as there's no manipulation or real disturbances to the cervix or anything. I mean, if you're having sex, your cervix is probably being touched, so....yeah...) I don't know if it would necessarily drop lower if you are dilating. It'll move forward before/with labor, but that's usually related to other factors as well, not just dilation alone. And also, one thing that caught me off guard about 20 weeks into my second pregnancy was funneling, which is really common with 2nd+ time moms, but scared me until I learned it! But because I became familiar with what amount of funneling was normal for me, if I had concerns later I was able to tell if that had changed at all.
So I think it's wise to know how to check yourself. But I know most won't agree.
This is a helpful link I found a couple years ago. I was already really familiar with checking myself but still found some parts helpful!
(all that said, while I've never been pregnant with twins, I have a TON of BH with my pregnancies, starting in the first tri, but they've never changed my cervix, even when I'm having a ton a day)