* You have assets that you want to shield from liability when your customers sue you -- you'd rather have them sue the corporation instead. But, no customers yet = no problem yet. Assuming that your new idea doesn't involve radioactivity or anything.
* You want to give away shares in your new business to angel investors, VCs, or partners. No investors = no problem.
In any case, if you really think you want to form a corp you should talk to an accountant, and possibly a lawyer, about the details.
If you need an entity for tax purposes, a sole proprietorship or LLP works fine.
It's a hassle to sell "shares" of an LLC to investors for capital, so I wouldn't bother because it the possibility is left open with a C-Corporation or S-Corporation.
Being a sole-proprietor or partnership doesn't limit your liability and investment doesn't really apply to either, so they're right out at the start.
And if you're just making something for yourself then there's no need for any of this.
Of course, depending on what you try to write off, the IRS might be very suspicious -- but that's true for corps, too. The rules about what constitutes a "business expense" still apply to corporations.
It does make the bookkeeping easier to have a corporation, and it may affect the odds of being audited, depending on exactly what your profits and expenses are. Again, there is no cheap substitute for a real accountant's advice.
As soon as you have to share (with investors or partners)
or to protect assets.But if u want to write-off ur expenses then its better u meet an accountant, most possibly he/she will suggest to inc.