Q: Yosemite store junk files and occupies more data

Go step by step and test.

1. Start up in Safe Mode.

    http://support.apple.com/kb/PH11212

2. Empty Trash.

   http://support.apple.com/kb/PH13806

3. Disk space / Time Machine ?/ Local Snapshots

  Local backups

   http://support.apple.com/kb/ht4878

4. Delete old iOS Devices Backup.

    iTunes > Preferences > Devices

    Highlight the old Backups , press “Delete Backup” and then “OK”.

    http://support.apple.com/kb/HT4946?viewlocale=en_US&locale=en_US

5. Re-index Macintosh HD.

   Do this twice. This will take a while. wait until it is finished.

   System Preferences > Spotlight > Privacy

   http://support.apple.com/kb/ht2409

6.Try OmniDiskSweeper. This will give the storage size details of the items.

   Select Macintosh HD and click  “Sweep Selected Drive” at the bottom.

   https://www.omnigroup.com/more

   Delete the files yo don’t want to keep.

   Be careful. Delete only the files that can be safely be deleted.

About “Other”:

http://support.apple.com/en-us/HT202867