The major benefit is that you can invest much more of your income into a SEP-IRA, which is a before-tax deduction. 25% of income or $75K, whichever is lower. That adds up.
But health insurance is a massive cost. Last time I ran the numbers, which admittedly was a while ago, my income as a self-employed consultant had to be much higher than my income as an employee in order to reach the same take-home amount.
I’m not a CPA and wasn’t interested in squeezing every dollar out of the system. I had a simple sole proprietor LLC. So there may be other tricks to pull. But the tax writeoffs are overrated, in my experience, other than the IRA. It’s not free money; for the most part, it’s a discount on purchases you wouldn’t otherwise be making, and a lot more hassle to boot.
Yeah, I typically charged double my salary rate. You have to pay for your own sick time and vacation time. I think that's generally baked in to the rate.