Sin6ularity: Why do you have hundreds of games installed?
I used to have only a few installed but found 9 times out of 10 I didn't bother playing the lesser popular titles if they weren't already installed, but would be more likely to play them if the bulk of the collection was. It's also a great feeling to have everything "on tap", 2TB SSD's have never been cheaper and older games take up so little space anyway. Alternative question - if you can, why not?
Sin6ularity: I don`t see the point of that unless your connection is not that great...
The entire point of GOG is that you don't need to re-download each game each time.