LiPo chemistry just doesn't like being stored fully charged.
The electrodes in the battery begin to break down.
Best case = It's no big deal
More likely = you lose a bit of top end grunt if you do it repeatedly.
Worst case = the cells swell and crack the casing and (possibly) burst into flames when you are using them.
It's just not such a good idea.
(FWIW, i sometimes leave a battery charged for a couple of days. If it was going to be a week, i'd discharge to a storage charge level.)
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