Network

Without a network you really can't play high level pokemon go.

No, we're not talking cables or wireless here.

When you're attacking a built gym you'll spend time and potions. If you're two attacking the same gym you'll spend less time and potions. And, you get to drop two pokemons into the gym rather than one.

When you're five people attacking a built gym...

Without a network you're always alone, or at least you can't plan ahead to get help with tearing down a rival gym, or to build your own for that matter.

So you need  means to communicate, and when you have the means you need something to communicate. What gyms to defend, which to attack, a day catching pokemon together rather than alone, an alert when a rare pokemon spawns, and so on and so forth.

Preferably you want to meet the people you play with, as in meeting them away from gyms and extraordinary spawn areas. In short, you need a hangout.

You want to agree upon times when you can play together and times when you can't. You want to coordinate when you do something fun and when you just want to grind together.

You need a network.

Or you're not playing high level pokemon go.