[question] Reason to use `u8` vs `u32`

I'm fairly new to lower level programming languages such as Rust and C. I was wondering what the point in being able to declare 8bit integers when they take up the same space in the registry as a 32 or 64 bit key. A lot of the time I only need \~1-100 as a range for a variable. Is there any point in using u8 instead of rust default u32?