In my opinion, scopes are one of the most under-rated tools, period.
I use them for tracking, mixing and mastering.
They are also outstanding educational tools which help you learn the frequency ranges of individual instruments.
To add to the above, for any kind of surround sound, a good scope is prerequisite. Over here we've got an RTW Vectorscope in prime position - always on. With its multiple settings, its an indispensable tool.