I thought this article was going to shit on the practice but was happily surprised that it does not. It's a good way to not only save on your bill, but it also reduces grid strain, in turn (theoretically) lowering maintenance costs for infrastructure.
Of course, it mainly only works if people are able to override (because then they wouldn't sign up at all) and it doesn't do much against huge data centers. Luckily in my area, there aren't any, but I'm sure I'm still paying part of their cost somewhere else.