Is that we need to leave at least 10-20% of free space for SSD?

[wdgann]

I saw people online mentioned have to leave some % of free space for the SSD health and speed, is that true and why?

 

[ShaBaz Khan]

this goes with HDD also...try to keep some portion free,

 

[hsyuts]

Very good read and answers your question:
http://www.anandtech.com/show/6489/playing-with-op

It talks about over-provisioniing (spare area) and how used space can be used as spare area.