[SuperViper]

In some callbacks, it's used to determine if an action should be completed or prevented. Take OnPlayerUpdate as an example, if you return 0 in OnPlayerUpdate, it'll prevent the new data sent from being synced to other players, where as if you return 1, it'll sync to other players.

In functions, it's usually used to return a certain value such as a player's admin level for example.

pawn Код:

GetAdminLevel(playerid)
{
    return playersAdminLevel[playerid];
}

You don't need return 1 here because you're trying to make this function return the player's admin level.

Return 1 isn't something you need everywhere, but you should have it in your functions and callbacks because lets say you're making a command and you feel lazy so you want to do something like

pawn Код:

return SendClientMessage(playerid, -1, "Hello world...");

This will run all of the code inside of the SendClientMessage function and it will return the value which is returned from the function SendClientMessage, which would be 1.