Are you in the US? If so, you can't save money on taxes by making less; it's a progressive system.
If you actually paid less in taxes on _every_ dollar by dropping a bracket, then you'd have been making more all along in a progressive system. Are you certain that was the case? Just curious.
I do the same thing (Australia). Worked 9 months last year and made about ~82-85% of what I would have working the full year, rather than 75%.
Incidentally this is why progressive tax is so important for a good startup culture (and thus overall tech scene). It's a negative tax on risk. The steeper your progressive ramp, the less of your geniuses are working in shit jobs creating UI form widgets with 40 managers telling them to redo it every other day.
In the UK, employers have to give consideration to reasonable requests for flexible working. But it also helped a lot that I work for a huge corporation, so they are better setup to deal with and permit such requests.
It was one of the best decisions I've ever made - it feels like I have so much more time for family, side projects and hobbies than I ever did before. And for reference, I work around 90% from home.
TBH, the company I work for has got a pretty good deal out of this, as I'm sure my productivity hasn't dropped at all. (it's a mega corp, so there is zero chance of negotiating back to equivalent of a 5-day salary)