r and f are usually pressed with the left index finger, which would have to move between keypresses. With r0, your right hand could align to press the 0 while the r is being pressed, saving time.
Solution: press both keys with a single "rolling" motion of one finger. I don't do that very often while typing, but when playing some games I'll hold down shift with the tip of my pinky and tap ctrl at the same time by flexing the middle of my pinky downwards.
I use a similar technique for typing all the symbols. If I press f I get f, r gives me r, but if I press f and r at the same time with my left index finger positioned between the two keys I get $. w and s are {, e and d are }.
All the other symbols, parens, etc. are mapped to similar one-finger-two-key shortcuts.
Significantly cut down on finger stretching which used to cause me mild pain.
