Macros are useful for automating procedures you perform frequently. You may also write macros that automate tedious one-time tasks.
Of course, not every task is a good candidate for automation. It might take longer to write the macro than to do the task by hand. If you don't expect to perform a task often, don't automate it. Also, automated editing procedures introduce an element of risk. You might not foresee situations that your macro can encounter. Incorrect macros can sometimes be destructive.
A little experience with macros and some careful testing will enable you to create a good set of macros for your own use.