A few things:
1. Jay's right, it's not a long-term strategy, it's strictly for hand-reading. Instead of playing your own hand it gets you to think more about ranges your opponent has, what you are representing, etc. No one's denying that without seeing your cards you are at a disadvantage and that if your goal is profit you shouldn't do it. But it can be a fun exercise to drop down and play a lower limit doing this
2. Some people saying who would know. That's kinda the point. If people know you aren't looking, it's kinda hard to represent hands. If they know you're not looking they'll just keep playing back and pushing all-in. Unless you want to start calling off a stack with literallly a random hand, you can't do anything about it.
3. No one's talking about straddles, people are talking about doing an entire session without once looking. It's not just one bet without looking then look, it's you play the entire time without looking at your cards. This forces you to basically win all your hands from your opponents folding (although I did actually watch one training video with holecards hidden where he made a call for value because he actually thought his range of ATC was better than his opponent's range, which he thought was composed of a lot of missed draws and no-pair hands).