Why not. I use Chrome to make quick calculations all the time. Just Ctrl+N and 1+1, and the answer is posted. Then Ctrl+W, and/or Alt+Tab to Sublime or whatever. Then I continue with my life :)
Aside from that, the most basic understanding of what Spotlight is reveals there is no other way for it to function other than to send the users input off-machine:
The user types in a value and results are returned related to that value, some, from online sources.
[0]: https://fcalc.github.io