The importance of an LLC is in the name: LIMITED LIABILITY. If you get sued they can only go after the assets of your LLC, not your home or your life savings. A sole proprietorship exposes you to unlimited personal liability.
The single-owner LLC acts exactly the same as a sole proprietorship for tax purposes. It gets "disregarded as a separate entity" by the IRS: You file the same Schedule C, make the same business expense deductions, etc. The only difference is you add the name of the LLC to the form.
For the liability protection to work you have to carefully keep all your business transactions separate from your personal spending. Otherwise in a lawsuit they could try to "pierce the veil" to go after you personally. Open a separate bank account under the name of the LLC and use it exclusively. Get a Visa debit card for the bank account. (Never use a personal credit card.)
As an extra benefit if your business gets audited by the IRS you can easily show all your business transactions by just giving them the business bank statement, keeping your personal transactions private.
You can always open a separate bank account for your sole proprietorship business. I would recommend it for anyone starting a SP. Also set up a separate company file in your accounting software. And keep all transactions separate.
Since the SMLLC files a Schedule C on the personal tax returns, it is combined with all other personal taxes if ever audited. If the IRS wants to audit the SMLLC, they will need the taxpayer’s Form 1040, including the Schedule C.
There might be some legal liability protection of a SMLLC, but not for tax purposes. Working 5-10 hours a week for a friend in accounting may or may not necessitate legal protection. That would be up to him to decide.