I forget which program it is, but I've seen at least one document editor where one click places the cursor where you clicked, a second selects the sentence it's

I forget which program it is, but I've seen at least one document editor where one click places the cursor where you clicked, a second selects the sentence it's within, and a third expands the selection to the whole paragraph. Combine that and modifier keys, and it's completely possible to have the mouse involved in intelligent actions, just not nearly as widely implemented as one might hope.