DTD Questions

I have searched high and low, and can't find these answers, so I'm hoping for some help.

I am doing my first DTD bodysuit, for myself. I keep seeing "DON'T CUT THE DUMMY". Any reason why? It seems rather...redundant to tape over clothes while I'm wearing them, then do the same for the dummy.

If my dummy stuffing is a bit lumpy (not terrible, just a little off here and there) is that a huge issue?

How does one do the measurement method? Everyone mentions it, no one explains it (that I've seen, perhaps I'm missing something? I did a rather thorough search before posting, but I could have missed something).

Thanks in advance!