I found at least 80 mg a day of thiamine got rid of about 95% of my chronic insomnia. Without it I get insomnia 3-4 days a week where I only get 3-4 hours of sleep a night. With it, I get 8 to 8.5 hours of sleep every night, and that's all I need.
It also gives me a very noticeable energy boost during the day. I'd like to try higher doses but I seem to be very sensitive to the thiamine.
It gives me a big energy boost but with that, if I take too much, I get a lot of anxiety. The anxiety I get with it, doesn't justify the extra energy I get, if I raise the dose.
All in all, as far as supplements go, I consider it an indispensable part of my protocol.