This is a requirement from the IRS. The IRS states: If you e-file your return but choose not to report each transaction on a separate row on the electronic return, you must mail the form8949 to the IRS.
After entering your transactions, complete and file your tax return as you normally would. Be sure to follow these extra instructions:
E-filed returns – Within three days after the IRS has accepted your return, mail the Form 8949 generated by TurboTax, a copy of the summary statements provided by your broker, and the Form 8453 generated by TurboTax, to the following address:
Internal Revenue Service
Attn: Shipping and Receiving, 0254
Receipt and Control Branch
Austin, TX 73344-0254
For more information please visit the instructions for form 8949:
https://www.irs.gov/pub/irs-pdf/i8949.pdf
https://ttlc.intuit.com/replies/4926553
