It makes your programs much easier to write and read, and probably makes them more robust because there are a lot of subtle and fragile assumptions that people often make in calling CopyBits, which CopyWindows takes care of for you. I would suggest favoring the fp.h routines since they are becoming standard. Note that VideoToolbox.h now automatically includes fp.h, if available, and otherwise includes math.h. This locks the keyboard so that the only way I can get back control is by using the programmer's switch. Alas, I've never had any need to write polite applications that gracefully share the computer with other applications.
Experiments always seem to deserve hogging it all.
The Sandstorm demo allows you to invoke other applications, because it doesn't obscure the whole window, but it doesn't act like a good citizen in paying attention to the messages it gets from the Finder about what happened. BlockMove is coded in each computer's ROM to implement the fastest possible move. E.g. it uses the MOVE16 instruction on the 68040 processor. It may be faster than the generic code that most C compilers produce. When the Quadra's were released, Apple added code to the BlockMove trap to flush the instruction cache each time BlockMove was called, just in case the move was copying instructions that were in the cache.