Can I get it to just pick a point instead of going through an entire document?
Yes. If you want to use Draftsmith specifically at certain places rather than the whole thing, for example, if you want suggestions for a particular sentence you can highlight a particular section of text before running Draftsmith, to just make suggestions for that area.
Draftsmith has a limit of 400 words at a time, so this is worth bearing in mind if you are highlighting a selection of text.