With the current so called solid state memory system (USB sticks, SD cards, SSDs etc) that use a managed storage algorithm the amount of free space affects the life of the device if run as a r/w drive.
Each cell (page actually) has a life of xxxx writes to it. the xxxx value varies amongst the chips used. They started off with a low 1000 write and now in low 10 thousands if I recall correctly.
So if one can have free space on the device then the memory management in the device spreads writes across the (free) cells/pages that have had the least writes.
Now if I have a 100GB SSD and 25% is files that never change and 25% files constantly changing (for an example only) and 50% free space. Then the simplistic management that just spreads writes across cells/pages with the least writes means that I get 3 times the life out of it compared with minimal free space
If the constantly changing amount is say 5% as one would have in the c: drive of windows. then for 45% unchanging files, 5% changing, 50% free we get 11 times the life.
So if the 5% change over 3 days and 10,000 writes per cell/page, you get 330 thousand days.
If the 5% is mostly OS cache then average change is on the order of 1 minute (v.fast for whole cache) for the whole. And you get around 200 days.
But rarely do we see those convenient ratios. For an SSD with 50% free space, you can expect a few years.
For an SSD used as a vault then one has to look at the on/off cycle time. A vault will mostly be static data rarely changing since they are chunks stored then only read, To compensate for potential dynamic control data for the vault, you only need to keep a good amount of free storage on the device. Say dynamic is 100MB worth then 2GB free is plenty, but all SSD devices should be left with a good amount of free storage for early cell/page failures on write attempts.
So if turn off once a day and can refill it fully then expect about 1/2 of the chip write count, due to dynamic data and possible early failure of some cells/pages. say 1000 to 5000 days depending on the SSD/SD/USB-stick used.