EVE Online is starting up a galactic event where the Sansha pirates invade sectors of space all over in Empire areas. The spawns have big groups of rats, like up to 50 battleships and even carriers. You have to fleet up to fight them though and you can get ganked while doing it... and not just by having your fleet be blown up by the other players.
You can be doing a site and another group can gank you out of the site. Like you're doing it with 5 friends in a fleet together and then a fleet of 100 come and blow everything up. Because the rewards only go to "the fleet that participated the most in the site in question" you have to be able to fight off the other players that are going to come and steal your site.
Or you can team up. You're supposed to form fleets. You want fleet bonuses, like 20% bonus shields or resists or damage. If you have someone in a command ship with fleet boosters and implants... even better. Plus they make being a fleet WAY more profitable. It's also good from a game design perspective because it encourages participation that might lead to social bonding, which in turn builds stronger player retention.