Lemmy.world and piefed.social are two different instances (servers) run by different people. They also run different software (Lemmy and Piefed respectively) which speaks the same protocol and can talk to each other (and other instances as well).
If you look at the same community e.g. [email protected] under each instance the content should be the same: the protocol should ensure that. The interface, the way it is presented to you, might be different, mostly decided by the software (Lemmy or Piefed, or any reader client you use).
It is also possible some posts or replies made it to one instance but not the other, perhaps due to technical problems, or policy (one instance’s admin might decide to not federate with another), but you should not encounter it very often (but it certainly happens).
People choose one instance over another for different reasons. Perhaps they like one software’s interface better than another. Perhaps they feel one server is faster and more responsive than another. Perhaps they would like to subscribe to a community which is blocked by certain instances. Fortunately there is nothing to stop somebody from signing up at multiple instances, so one can just try each out and find out which one is suitable for them.
Lemmy.world and piefed.social are two different instances (servers) run by different people. They also run different software (Lemmy and Piefed respectively) which speaks the same protocol and can talk to each other (and other instances as well).
If you look at the same community e.g. [email protected] under each instance the content should be the same: the protocol should ensure that. The interface, the way it is presented to you, might be different, mostly decided by the software (Lemmy or Piefed, or any reader client you use).
It is also possible some posts or replies made it to one instance but not the other, perhaps due to technical problems, or policy (one instance’s admin might decide to not federate with another), but you should not encounter it very often (but it certainly happens).
People choose one instance over another for different reasons. Perhaps they like one software’s interface better than another. Perhaps they feel one server is faster and more responsive than another. Perhaps they would like to subscribe to a community which is blocked by certain instances. Fortunately there is nothing to stop somebody from signing up at multiple instances, so one can just try each out and find out which one is suitable for them.