My take - biocides are never a bad idea, but are probably more important if your truck sits for long periods of time giving the critters a chance to grow. There are many biocides on the market that get decent reviews, and they're not that expensive per treatment. I use Stanadyne - it was referred to me by one of the fleet guys where I work, and a jug lasts me a couple years.
Additionally, a tank of B100 on occasion will keep things very clean. Biodiesel is an excellent solvent - I run a tank about every six months, just prior to servicing my fuel filters.