First the values on the paycheck and W-2 almost always differ somewhat and the IRS wants an exact match. This can delay any refund by weeks.
You also will not know what to enter for the various boxes on the W-2.
If you mail file then you are required to attach a copy of the W-2 to the tax return or the IRS will return it to you unprocessed. While you are not required to submit W-2's with e-filed returns, you still must have the W-2 in your possession since the IRS can ask for it when they review your w-filed return.
If you do not receive your W-2 by February 14, then you can use your paycheck and file a 4852 form, but you must follow the IRS rules in order to do so.
[Paraphrased from IRS rules]
Can you file without having received your W-2? Yes, but only if you have not received it by February 14, and you have contacted your employer and attempted to obtain it, and you still have not received it by February 14, and then you contact the IRS (see the link below), then if the IRS is not successful in getting your W-2, you can use form 4852 in place of your W-2. But you MUST speak to the IRS before doing so. Otherwise, you cannot file before you receive your W-2.
http://www.irs.gov/uac/Here-is-What-to-do-If-You-Are-Missing-a-W-2
The IRS will not be processing any returns before Jan. 23 anyway, so there is no advantage to file before that - it will just sit on the TurboTax server until the IRS is ready. If you discover anything that needs to be changed or added in the mean time, you will not be able to change it. Once you e-file it is like dropping it into the mail - it is gone and cannot be retrieved.
Also see this excellent post on the subject:
https://ttlc.intuit.com/questions/3405095-tax-refund-schedule-and-filing-with-paycheck-stub-without-...
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
