Suppose you wanted to switch between C/10 and C/20 charge termination? The Powerlab can do that with the default presets. The 306b is a multistep non-intuitive process to change values.
By far the 306B is much easier to use over the PL8.
Suppose you are going to parallel charge two 4400 packs. The next time you want to parallel charge four 4400. On the Powerlabs you use the same preset, same current setting, just changed the number of packs in parallel and go. With the 306b, do the math in your head, hope its right and press the buttons several times to get to the new value. Not difficult, but not near as simple as changing the number of packs in parallel.
Suppose you are done parallel charging your four packs and you want to know the average mah you put back in each pack. The Powerlab does the math for your and gives the average for each pack. With the 306b, break out your calculator. Not hard just not as SIMPLE as the Powerlab.
Suppose you want to put the packs at storage voltage. The Powerlab uses a CC/CV discharge and will hit the target voltage every time. The 306b may end the charge prematurely leaving the pack higher than the desired voltage, require some fiddling to get the desired voltage.
Suppose you want to tweak the charger settings at the field. The Powerlab's setup menus are intuitive and are easy to navigate. Its easy to go forward and back through the menus. With the 306b having the manual handy or memorizing the giant flow chart in the manual is a must. Menus and navigation are not intuitive.
Suppose you just want to enter a desired charge rate in C (1c, 2c, etc), then monitor fuel level of the pack during the charge given in a percentage up 100%. Very simple to do with the Powerlab. Not even possible on the 306b.