Keep your coins

Some folks like me hate coins and want to get rid of them as quick as possible. Over here that is not a good idea. For example using the Colectivo (bus) you need to have coins. Otherwise you will have to find other means of transport. Some bus stations have personnel who give out tickets before boarding the bus. This is done to speed up bus departure times mostly. With small bills (2 and 5 peso) you can also buy a ticket at these points.

If a shop is out of coins and they ask for it and you don't have any you run the chance that you will get less money back than you should. This depends on the policy of the shop. This also happens to me once in the subway. Forget complaining then. In mentioned case it's either pay more or just not use the subway.

Further for using phone booths on the street it's also a good thing to have coins. Unless you have a phone card. Pay phones with coins are way more distributed than the card ones.

Finally since giving tips is pretty institutional it's a good things to have coins after for example taking a coffee somewhere.