"loop" can all be typed with one finger, as the letters are all together on the qwerty keyboard, and the "o" repeats itself.
"while" on qwerty is sort of a chore.
Usually for speed and avoiding strain you want to incorporate as many fingers as possible. In fact it's a common mark against dvorak online that "ls -l" is all typed with the right pinky (not an issue in the workman layout luckily).
Using more fingers allows for faster typing.
When you can touch-type, it's better to have keys spread to use separate fingers. That way, you divide up the work. You have one finger still lifting while the other's already starting the next press.