HUD doesn't gather anything that human's eye / mind can't notice, if you play one table live/ online and pay attention, you can definitely do just fine without HUD.
When HUD is useful, is when you're multirooming / multitabling online, different tournaments, different opponents, different stages of tournaments at different tables - it's good to look quickly on stats and don't put a ton of attention/ concentration to try and recall what this CO on table 6 is playing like / what his stack is / what stacks of whole table are /should you repush or fold cuz it's bubble here while the game at table 3 has just started. You can use your time on actually thinking about your decisions and not trying to figure out this basic stuff. Obviously when you're playing one table live, you already know all of this before facing a decision, as you don't have any other sources of different information that distract you from this table. Therefore it doesn't mean that you posses some special skill if you can play fine one table without HUD live or 2-3 online.
In addition, if you're multitabling online after the same amount of time you will play a significant amount more hands over the same time you will do playing live, thus you can using your HUD to analyze your own game. Around 100k hands are more or less enough to find some tendencies and patterns and correct them if needed. How many years you will play this amount of hands live?
Variance play a huge role in live poker especially in MTT.
So HUD is neither good nor bad in the long run. It's essential if you're multitabling; it's useless if you don't know how to play. Maybe it will help to a solely online player to start playing a couple of tables online without HUD if he's planning on transitioning to play live only, just to get used to keeping all the info in your head, and that's it as I see it.
