Question About m.2 SSD

to completely remove the I/O bottleneck when performing read/write requests to a storage medium, the faster that storage medium is, the better.
so putting everything on the SSD is the ideal solution.
however, SSD's costs more than HDD, although they are dropping every month, SSD's still cost considerably more per GB than HDD.

so typically you would get a smallish SSD, say 256GB, and load all your programs on that.
and get a 2TB or so HDD and storage your data (docs, pics, vids, downloads etc) on that.
that gives you for example, the PC and Word starting blindingly fast and then normal speeds to open your documents.

and SSD size and cost permitting, you would than put your docs on the SSD too to get the best possible speeds.

games as you would know take up a lot of space quiet quickly. install 5 or so games, fully patched and updated, and watch your SSD space disappear. so wither get the biggest you can afford, or install them onto a HDD. you should also be able to install the game onto the SSD and tweak the settings so it dumps all screen shots, saves and the like onto another location of your choosing.