There are times when you are writing a query while referencing another piece of information: the results of another query, a variable value, a webpage, etc...
If using two monitors you can have a query window on each as a reference, or you can resize two query window tabs so they both fit on the screen. But did you know there's a better option?
Vertical Tab Groups
Vertical tab groups are great because they stay contained within the parent SSMS window. This is nice for when I'm working on a small laptop screen or don't want to receive whiplash from moving my head back and forth between two monitors.
In order to create a vertical tab group, you need to have at least two query tabs open. Right-click on the tab you want to be on the right-side of of the screen and choose "New Vertical Tab Group"
You can easily change the size of each open tab group by dragging the divider between them:
If you are working with really wide data, you can also try a horizontal tab group instead:
My favorite feature of tab groups is that I can move my entire SSMS window from one monitor to another (or minimize it) and all of my tabs follow suit. This comes in real handy if working on multiple different projects at the same time.