Comma-separated expressions
- Use them only where it really makes sense to do so.
- Use them only where it really makes sense to.
- Use them only where it really makes sense.
Which one sentence I should use? Are all them grammatically correct?
All are correct/acceptable.
I’d probably use the first example, favouring it over the second example only because the latter feels a little abrupt, especially when written, though this could just be personal preference.
The third version is also acceptable, but to me could be seen as ambiguous, i.e. it could also be written as:
Use them only where they really make sense.