What are the benefits of SUB 2 financing a property?

Unless the property needs work and the seller is desperate, you're not going to find a seller willing to do any sort of seller financing on their end. 

I plan to offer owner financing to others that can't get a loan.

Quote from @Guillermo Perez: Does anyone have experience with seller finance?

The main condition was I had to have the downpayment (20%) first, close the deal, and then execute the owner financed 2nd mortgage. 

I have an opportunity to purchase a mixed use property that seller is open to using partial seller finance.

We are about to put in $15-$20k of our own money into it, beyond what insurance covered and I need help deciding how we should finance it. 

Purchase price: $98,500 Cash invested: $15,000 owner financed on duplex, bought from a friend of the family. hopefully many more to come

The owner is open to seller finance for us.

Two separate property appraisers (at the direction of the lender) were sent out to appraise, and neither was willing to appraise it as a "residence", and thus financing fell through (conventional primary loan).