Multiple selections let you make sweeping changes to your text efficiently. Any praise about multiple selections is an understatement. This is why:
Select some text and press Ctrl + D to add more instances. If you want to skip the current instance, press Ctrl + K, Ctrl + D.
If you go too far, press Ctrl + U to deselect the current instance
To add all occurrences of the current word to the selection, use Find All: Alt+F3 on Windows and Linux, or Ctrl+Command+G on OSX.
Multiple line selection to Single Line
Command + Ctrl + L to select multiple lines, Ctrl + j to join in a single Line
Edit Tags simultaneously
Just hit Cmd+Shift+K (on OS X) or Ctrl+Shift+’ (Windows and Linux) to select both tags for editing.
Open a File - Command + p