Does mac need minimum 10-20% free disc space on primary drive like a windows system does? I seen many windows machine crawl or die due to lack of this overhead. I ask as i'm going fit a small ssd to my imac and wounder if it be too small. At present if I remove all my files from home folder will only need 29GB on primary. Going to fit a 64GB SSD. also got photoshop and dreamweaver to install yet.