Your Mac needs adequate hard drive space to operate normally. How full can a drive be before it's too full? There is no hard and fast rule that says “X” amount or “%” of free drive space is needed. A low amount of RAM requires more drive space for Virtual Memory’s swap files.
Problems from insufficient RAM and free hard disk space are discussed in this link
Here’s some general guidelines for minimum hard drive free space:
1. As a general rule, your available space should be 5GB as an absolute minimum as it generally requires that much free space to perform an Archive and Install of Mac OS X and still preserve some free space for VM swap files.
2. Some say that your hard drive should have at least 5% of it's capacity available for use. Still others say 10% to 15%. If you routinely process complex graphics and videos, even more space is required.
With your 19.7GB of free space, you should be OK. Usually it's best to not state a percentage, but state an amount of free space. There's a big difference in having 10% free space (20GB) on a 200GB hard drive compared 10% (4GB) to a 40GB hard drive.
Look at these links about freeing up more space.
Where did my disk space go?
Download & use
described in this link or
Disk Inventory X
Freeing space on your Mac OS X startup disk
Amazing Disappearing Drive Space
Increase HD Free Space
How to free up my disk space
Cheers, Tom 😉