Its typical that the most likley time you are ever likely to run out of ink is when you have something important or urgent to print. So its always a good idea to have a replacement of each colour available.
If you can afford to buy in bulk its a little cheaper to buy a whole set. Saves on postage at the very least!
I have always preferred to buy the Epson original inks - more expensive than compatibles but in my view give better results.
For me, the only down side of buying this bulk set is that my 4+ year old R800 was beginning to show signs of age - needing frequent recalibration and head cleaning. And I could have bought a whole new (Canon) printer for less than the cost of this bulk set.
So in finishing this review, these Epson inks are the best, and the R800 is a fantastic printer but if yours is more than a couple of years old and getting temperamental ask yourself if you should be buying all your inks in bulk.