Why are binary numbers almost always grouped in 4 bits?

Question

I'm learning ARM so going back to basics with binary/hex arithmetic and it got me thinking about how binary numbers are usually presented in groups of 4, e.g.

1111 1110 1101 1100

Is there a particular reason why it's done this way? Seeing as we normally describe memory in terms of bits/bytes/megabytes etc I'd have thought they'd be better grouped by 8?

Answer 1

One reason is that it becomes easy for representation and conversion into Hexadecimal. One Hexadecimal Digit consists of (represents) 4 bits.