With modern lithium batteries, running it all the way down and then fully charging is not necessary. This may have helped with older batteries, but running a modern battery all the way down risks fully discharging it, which is irreversible. It's unlikely to happen, since there are safeguards, but if someone ran their battery down and then forgot to recharge for days, then the battery might completely die. To be honest, I wouldn't rely too heavily on Best Buy staff for tech advice.
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