When you have a few minutes and are bored, watch your charger at those different charge modes: balance, fast charge and charge. Notice that in all, you set the charge amperage and basic rate. My understanding is that the difference is at the end of the cycle. Chargers taper off the rate while topping off the battery. Different modes use different length taper, and correspondingly fill the battery a little more or less. On my charger, I can set the taper rate but most use set rates. Some examples are C/3 for fast charge to C/10 or C/20 for a slow balance. C = charge rate in this case. For a charge from storage (basically a half charge compared to after flight) a large part of the time can be in taper balance, so if you don't need every last milliamp in the cell, fast charge. If comfortably are above 20% after flight, then charge then fast charge. You might get 1 or 2% less full, but if you have enough, that is not a bad thing for the battery, and is faster.
I try a faster taper to save time, and check the time vs regular charge. That is my first preference over higher rate. High rate may also hit peak before slow rate, and save some time at a couple less percent input, but high rates aren't great for the battery. But time saved is flight time :-)
If you parallel charge, balance is somewhat poor unless the batteries are fairly well matched. You are only balancing the batch of cells on each pin but you can get some high and some low.
But, as WD noted, higher rate will lower time, so fast charge at high rate if time is your priority. Battery life cycles may be shorter.