BCD mode is useful when you are working with numbers that you want to display to humans often. That is, you can do all the arithmetic in base 10 instead of binary. BCD is slower to work with than binary, but much faster to convert in and out of, since there's basically no conversion other than adding 0x30 (ASCII '0') to the nybble you want to display.
Working in binary, on the other hand, requires costly conversion in and out of human-readable decimal. For example, converting decimal to binary requires a costly multiplication (by 10) on each digit consumed, and converting back to decimal from binary requires a costly division (by 10) one each digit produced.
So for things like scores in games, yeah, BCD is a nice thing.