I'm new around here and to diesels in general. I'm obsessed with car forums, however, so I like to read up on the quirks of our engines. All that reading has driven me to my current strategy. I am by no means an expert.
I use additives due to the conventional wisdom that ULSD (Ultra-Low Sulphur Diesel) mandated in the US isn't the best for our engines. Unlike with gasoline engines, many parts of a diesel engine's fuel system are lubricated by the fuel itself. ULSD doesn't lubricate as well as some would like, so using lubricity additives like biodiesel, PowerService, etc. is meant to compensate for that.
B2 (2% biodiesel) seems to be the lowest concentration of biodiesel that has the most dramatic impact in increased lubrication. More that B2 seems to have diminishing returns, that is, B5 is only fractionally better than B2. For those of us who have to manually add biodiesel, B2 is a practical concentration to use: one quart biodiesel per tank - B5 would require 1.25 gallons per tank - a bit much to carry in your trunk.
Additional additives are probably overkill for those of us using B2 in high cetane states like TX, but they won't hurt.