If you are a single member LLC or single member S Corporation, you are what's called a "Disregarded Entity" under the tax law. This basically means that the IRS does not see your S Corporation or LLC as a separate entity for tax purposes, despite the fact that entity still provides you limited liability for corporate purposes.
For tax purposes, disregarded entities are simpler to report than S Corporations and LLCs. Normally, S Corporations and LLCs would have to file two sets of tax documents: 1) Their own corporate tax return (1120S or 1065) and 2) K-1s to the shareholders/members which show how much information each own. Then, the individual has to write down how much profit/loss they make on their personal income tax return using the K-1s.
Disregarded Entities, on the other hand, can report all of the gain and loss on Schedule C of the individuals 1040 personal income tax return. This means that no corporate tax return and K-1s are required, which saves time and paperwork.
In addition, you are considered to be a disregarded entity by default when you are a single member S Corporation or LLC, no additional tax election is necessary. Therefore, the simplified reporting makes your life easier by not requiring an election and by requiring you to file less documents. Therefore, you should consider using the simplified reporting of the disregarded entity if you are a single member S Corporation or LLC.