What is the advantage of bottling a bounty rune?

Why do people with bottles yell at and/or ping the hell out of me when I'm about to pick up a bounty rune, giving the explanation "I have a bottle" or "Bottle ready"?

Why does having a bottle make one the better recipient?

Solution 1:

Bottling a bounty rune automatically refills the bottle to 2 charges, making it a very useful way of refilling your bottle without going back to the fountain or sending it on a courier. This leads to better lane sustain in general, especially since the bounty runes spawn every 2 minutes. (Also note that powerup runes refill the bottle all the way, making them even better for this purpose. They spawn less frequently though.)