Does my supplemental business expenses worksheet need to be attached to my return when filing by mail

Only include the forms/schedules necessary for filing with your tax return. If anything needs to be attached, it will say so on the filing instructions page that print with your return. You can print/keep worksheets and supporting documents with your tax return copy for your records.

Note: Not all forms are ready and available to print at this time. Check the links below for form availability before you attempt to print.

https://ttlc.intuit.com/questions/1908854-irs-forms-availability-table-for-turbotax-individual-personal-tax-products

https://ttlc.intuit.com/questions/1908857-state-forms-availability-table-for-turbotax-individual-personal-tax-products

But is that form necessary. that's what I'm trying to find out.

No. Just keep for your records.

if its not necessary, then why its included in the printout?

Worksheets are for your records ....  you only attach forms, schedules and statements.