The lure of solo practice from my perspective is the ability, like most small businesses, for the owner to defer a huge amount of cost and taxes through transfer pricing. That is if you have a good accountant or a good background in accounting, you can get away with paying virtually no taxes legally. A solo earning 150-200k, where I am, is earning much more (after taxes) than any non partner in big law.
Tax lawyer here.
Regarding transfer pricing:
If anything, most solos are going to pay more tax because of self-employment tax. Barring fraud and/or some really "creative" return positions, very few are paying "virtually no taxes"- and it's not because they aren't accounting mastermen.
You may be a tax lawyer, and you may be right legally, maybe you are not. But "Creative" accounting is very common.
There are U.S. tax lawyers who say you are not even legally required to pay taxes (not saying I agree with them, but the tax laws are written in a purposely vague way that is open to interpretation). Heck just take the term INCOME taxes. There are tax lawyers who argue income = revenue - expenses, and since Income tax is voluntary, if you voluntary overpay by miscalculating your income as revenue, the government is going to say its your fault for calculating wrong. Now I am not saying this is my view, but this is just an example of what one US tax lawyer argues.
I've worked in a Finance firm that use to provide advisory services on taxes to firms looking to reduce tax loads. While I did not engage in this, I can tell you we have accountants and lawyer, and accountants who are tax lawyers with LL.Ms; and its normal practice for firms to use transfer pricing to avoid paying taxes. There are quiet a few major companies doing this, and the firm has advised numerous American based f-1000 companies on this. Transfer pricing is not illegal unless the government can prove the sole purpose of you transferring is to evade taxes (tax evasion/avoidance) and in the U.S. the tax law is far more lose (no specific statute that criminalizes tax avoidance only tax evasion = not paying taxes or lying about it). In Canada it is a crime to undertake acts for the sole purpose of reducing your taxes (Called tax avoidance). In fact CBS did a documentary on US firm locating headquarters in Switzerlands, which were just mailboxes or empty offices, where they would claim they transfered all their income to.
I'm not an accounting whiz, but I can tell you tax law for businesses, is akin to how Jack Abramoff views lobbying rules in Washington. You have alot of silly rules, that more or less parallel saying you cannot give a congressman money standing up but you can give it to him sitting down. You cannot give a congressman a hamburger for dinner, but you can call it a fundraiser and give him a cadillac and a steak.
Especially given the fact that US law firms can incorporate or the rules have been more relaxed on that issue, it is extremely easy to transfer price money. This is the real reason why $10 trillion is offshore.
Also US partnership firms can elect to be taxed as a corporation. So all the corporate tricks apply for partnerships. Only Individual income, if you believe that you do have to be taxed which I do, really have to pay income taxes.