It's true that the frame makers (or the people who make the BB insert) can machine a BB30 bore in a single cut, making it easy to get it precise and aligned. (there are also circlip grooves to machine). That's a good thing for us. It means that frames no longer need to be chased and faced before being built. And a design that makes precise manufacturing easy means that the frames are more likely to be made precisely.

Some carbon frames make the BB entirely out of carbon but often there is an aluminium BB insert for the BB30. They always have an insert for BSA ("english threaded") BBs. Bonding the insert to the carbon has sometimes been a problem in the past. But it's mostly solved now.