How to Clean Startup Disk on Mac
Mac asks to clean startup disk when storage is almost full
Step 1. Apple menu → About this Mac
Step 2. Click on the storage tab
Step 3. Click on Manage
Step 4. See the recommendations
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a. Store in iCloud → This frees up space from mac and puts files in iCloud. You can choose what all goes to the cloud among the options given.
This will not delete your files, just store an optimised version wherever applicable.
b. Click on Optimise storage to automatically delete videos after watching from iTunes
c. Empty trash automatically after 30 days
d. Click on review files to see files ordered from largest to smallest and delete redundant large files