No it's not necessary but it does aid to breaking up the sediment that gets in them.
A baby food jar and some Rosonol Lighter Fluid is all you need, or Coleman fuel (white gas).
Make sure the bearing doesn't have an orange seal or some other crazy shielding that might melt in the cleaner.
Let the bearing soak. Then swirl around and let soak. I would then take the bearings out and put them on the end of a pencil and spin them with a flick of my finger and then re soak. Only a few minutes are needed. When the bearing will spin to your liking, blow it dry and put a drop of oil on it.
I use a magnasonic cleaner now, I don't remember how much it cost.