The cost is pane switching. The upside is, having chrome logged in means I get persisting clean history when I want it.
This seems to be a very common use case among my friends as well - they all have at least 3 Google accounts out of which they only use one account for chrome linking.
From what I understand, you're asking how you can just "temporarily" log into an account — can't you just add that account as a new user on Chrome?
If not, you can always open an incognito window or a guest window, do your business, and close it. I do that often when I'm logging into an account that I don't want to persist.