I'm trying to wrap my head around grave accent (`) and its use in Houdini.

If I use this as an expression, then why do I need to have it inside the accents as an example `npoints(1)`?

The backticks from from unix shell scripts. The mean ‘evaluate me first’. They are not needed in an expression keyframe, as they are always evaluated at the current time.

Entering non-numerics into a float or integer parameter will create a keyframe with the text as the expression for you, which is why backticks aren't needed in that case.

In string parameters, since text is always entered, there's no reason to automatically add a keyframe. This is why backticks are needed if a keyframe hasn't been manually added. The backticks cause the text inside to be evaluated instead of used as a literal string.

A grave accent sounds like something a Bond villain might possess.