Whenever Time Machine backs up your data into the external hard drive, it defaults to saving copies of the entire contents of your Mac’s hard drive on the target disk drive. That’s okay if you are just working with a small amount of files. However, as your internal disk drive fills up, each backup will take more and more space.
You can actually specify which files you want to back up. Or rather, the more correct term would be you can identify which files and folders you want excluded from the Time Machine backup. Most of the time, the folders containing important files like personal documents, photos, and the like, is the one that should be the backup priority.
To exclude files, folders, or even volumes from being back up, launch Time Machine and select Options. A pop up sheet will appear. To identify the files or folders to be excluded click the + sign on the lower left portion. Identify which ones you want to exclude. You can go as deep into your directories to identify a specific file. Or you can be shallow and click a main directory such as Downloads or the Applications folder. Just continue clicking the + symbol to keep on adding files and folders. Highlight a specific entry and click – to remove an entry from the exclusion list. Confirm settings by clicking Save.
The next time Time Machine backs up it won’t save the items you put on the exclusion list.