I have boards built to parallel charge some of my smaller packs. It can be great, but it can be a pain as well. Mostly the batteries have to be really close in voltage, and if for some reason they aren't (different flight times, or different kinds of flying) then parallel charging can't be used. Some people will hook up to discharge a pack to a voltage to match, but that adds another step instead of just charging. If you rely on this kind of charging to keep your packs full in the field it is easy to think you can charge 10 packs at a time and end up having to charge them one at a time anyway.
These is also the concern of total watts to the charging port. Most charges that will charge 4 batteries at a time basically have 4 50 watt charges in them. Add a power supply with enough power and you can charge 4 2200 mah 3S packs at 2C and not much more (it would be a fraction of a volt more and I don't think that really matters). So, if you want to charge 8 2200 mah 3S packs you could charge 2 of them at 1C on 1 port, or split them up and charge them at 2C each and not have to worry about following any additional rules like making sure they are close together in voltage. The timing is the same (or close to it) and less equipment is required. If you have a much high watt rating on your charger it might be worth it, but I really haven't seen too many reasonably priced charges with more output than that.
Basically this is great for very small packs. I charge 6 210 mah 2S packs for my UMX Beast on one port at 1C. These batteries aren't rated for a higher charge rate, and each pack needs less than 2 watts of the 50 each port is ok putting out. In this case the time saving is worth the trouble. The law of diminishing returns plays a large role here.
