I've attended a UFC event and a WEC event. Honestly, the only thing that makes it worth it IMO is getting the chance to meet and and interact with the fighters. Other than that, its harder follow the action at the event than it is on your TV, its less comfortable at the venue than it is in your living room, if you get up to get food or go to the bathroom you may miss a flash KO or something, and when I was there I was so caught up in the atmosphere that everything kinda wizzed by. at the end of the night, the only fight I could rememeber when I thought back on it was the main event. Plus, if you order it on TV you can DVR and rewatch whenever you want.
That being said, I actually WOULD recommend going to at least one event for the experience of the atmosphere and meeting the fighters. And if it's an event with a card you're not that interested in, thats perfect, cause you won't be missing much if you can't follow the action and don't have it recorded on your DVR.