Basically, deadband is the smallest amount of movement the servo can resolve. The smaller the deadband, the higher the accuracy. It is similar to removing some "slop" in your linkages when you reduce deadband.
The Hitec servo programmer (HFP-10) costs about $150, but if you have lots of servos or can borrow one it's great. You just need to reprogram a servo once and it's like that from then on (sometimes you can get the dealer to program them before sending them to you).
The programmer will allow you to tweak deadband and probably a dozen or so other settings, and test a bunch of things with any brand servo. It will also measure the signal from your receiver so you can see exactly what pulse width it's putting out (i.e. 1500us center, etc).
Back to the topic...Hitec servos come from the factory with deadband set to "2" as I recall. The programmer allows you to set them to the lowest value of "1". This also helps the servo be a bit "firmer" to hold it's position. Most people find the Hitec's to be soft in this area, so this will improve them slightly.
Hope this helps!