Yes, an SSD significantly improves performance for MAC OS YOSMITE.
Yes, an SSD significantly improves performance for MAC OS YOSMITE.
Yes, an SSD significantly improves performance compared to traditional hard drives.
Based on my observations, SSDs boost OS X performance more than they aid Windows. You should definitely think about getting one. It works well with a solid-state drive, but slow spinning 5400RPM drives have trouble keeping up.