When you switch factions in an MMORPG, there are usually a few different things that happen. First, if you have any gear or items that are specific to your old faction, you will usually lose access to them. This means that you'll have to get new gear for your new faction if you want to be able to use it. Additionally, you may find yourself unable to do certain quests or activities that you could before - this is because the game's content is often divided up between factions, and switching sides means losing access to the content on the other side. Finally, depending on the game, switching factions may also mean giving up any progress you've made with your old faction - so if you're close to max level or have grinded out a lot of reputation with them, switching may mean starting all over again from scratch.