Modern SSD’s can take about 100,000 writes. Your mechanical hard drive will probably fail long before that, especially if it is set to never sleep. SSD’s don’t need to sleep.
I have had a bunch of OWC SSD’s fail too soon. Lately I have been buying Samsung - 512 GB, 6G drive for around $350 on Amazon.
The performance boost is so dramatic that I would never again spec any computer for my company that didn’t have an SSD boot drive.
I am typing this on a 15" Macbook Pro with 750 GB 6G SSD (Samsung I think). Getting 450 MB/S read and write times. 7200 RPM mechanical drives get about 100 MB/S over internal SATA, maybe more on 6G.
I use to keep projects on a second internal mechanical drive on my Mac Pro, but now I run them from an SSD boot drive and archive them to the other drive.
In two years mechanical hard drives will be dinosaurs.