One reason might be to acknowledge that you're not being prescriptive, but leaving room for a subjective POV in situations that call for it.

Likewise, the GP's use of "actually" acknowledges the contrast between what one might expect (that some preliminary type-checking might happen during initial parsing) and what in fact happens (no type checks occur until the template is used.) It doesn't seem out of line in that case.

I agree but it's not always clear whether you're stating an opinion or attempting to state a fact. Some folks would reply to a comment like this with "citation needed" but wouldn't otherwise have said that if the comment had opened with "I think."