Michigan Sales and Use Tax Certificate of Exemption

[CornerstoneAcre]

I am wondering if anybody uses a tax exempt status for their farms? What are the pros and cons of going this route? (I KNOW- ask a tax professional!! I most likely will, but wanted actual "user" input first) This is an exemption that allows me to NOT pay our 6% state sales tax on certain agricultural supplies.
I have form 3372 but unsure of what section 3, line 4 means when it asks for %? If our ONLY income comes from farm - would it be 100%? If our MAIN income comes from farm - would it be say 80%?

[Maura]

I went to the www.michigan.gov website to look up this form.

And yes, if your income only comes from farming, then 100%. If one of you works off the farm, do the math to find the percentage.