Simply right-click a file in Time Machine and choose the option to delete all backups of it. However, backing up large data sets reduces the number of backups a smaller drive can hold, so if you want to keep more Time Machine backups available, you don't want to keep backing up large and unnecessary files, such as a copy of a movie you don't plan to watch again. In this way, Time Machine can maintain extensive snapshots of your system over time. This routine should ensure that even with a relatively small backup drive (at least the size of the collective data you are backing up), you will have ample system restore points and access to prior versions of files.
Apple's Time Machine feature is a full-system backup routine that will maintain hourly backups for the past day, daily backups for the past week, and weekly backups for as long as there is space in the drive to store them, and uses a feature called 'hard linking' to share unchanged data of previous backup files with new files copied to the backups.
