This is regarding the Qualified Business Income deduction which is new for 2018. Business income from self-employed businesses can qualify for a deduction up to 20%. But, specified service or trade businesses (SSTB) are excluded from the deduction if one's taxable income is over certain thresholds (starts phasing out at taxable income of $157,500 single or $315,000 joint), therefore this information is being requested on all returns with self-employed income. See more information on the Qualified Business Income deduction below, including examples of an SSTB, plus another link with information on whether rental activity will qualify for the deduction.
https://ttlc.intuit.com/replies/7019998
https://ttlc.intuit.com/replies/7122193