Another one for the oh-so-obvious file, the Add Rows And Columns app allows you to -- you guessed it, Sherlock -- add any number of rows or columns to your Google Sheets spreadsheets in one fell swoop.
Lest you think that's a strange thing for an app to do, remember that Sheets provides the ability to insert new rows and columns only one at a time. If you're trying to add a large number of rows or columns at once, it can get tedious fast. (You can, of course, add as many rows to the end of a spreadsheet as you like in one fell swoop natively with Sheets.)
In addition to the oh-so-obvious file, we should probably file this one under "Filling In Obvious Gaps In Functionality." As this list of applications reminds us, that's a critical file to keep full.