Power-Ups give you added features and integration options. Each free account allows for one Power-Up per board. You may use different Power-Ups on different boards.
The Google Drive Power-Up allows you to link directly to files and folders within the drive. This can be handy if you have large files that are unable to be imported into Trello.
The Google Drive Power-Up gives you the option to turn a board into a Google Slide Presentation automatically.