The original consideration for the cradle is that you can put the portable in the cradle, and it'll recharge. Then you just remove it when the charging is done. There's no real need to touch anything else.
In other words, you don't have to take the battery out, put it into the charger, and put it back into the portable when it's done.
Pre-cradle Sharp models have always recharged in the unit itself, though. So the only reason for cradle is that you don't have to plug/unplug the AC adaptor into/out from the MD portable. When Sharp first came out with cradle models (831/531) they told reporters that they found this popular with the customers.
Any other feature that seem to have come with the cradle (e.g. refresh) does not necessarily require the existence of the cradle
While older Li-ion Sharp models required 5V power into the unit itself, the Ni-MH Sharp models (MT66/77/770/880) isn't requiring as much. So the cradle also includes a DC/DC converter (5V-->2V in the MT770's case) so Sharp can continue to bundle the same 5V AC adaptor with their portables.