Deleting Local Backup Last Week I found that the local backup took about 20-30 GB free space on my MacBook Air and I deleted them using:

sudo tmutil disablelocal


I weekly backup my notebook using my external harddrive with Time Machine. Was it important to keep local backup on my Mac and spare 20-30 GB space or because I weekly backup to the external drive, it is not necessary to leave it open ?
Unless you are traveling and won't have access to your external backup drive, disabling the local backup is OK. I would backup your laptop with more frequency, however, unless all your data is stored in the cloud somewhere.

Lastly, if you take your laptop to work regularly, keep a second external HD in your desk and use Time Machine to create a second backup.