sub 2 is an acquisition technique. it menas subject to taking over existing mortgage payments, liens, encumberances, taxes, insurance, etc.
you can find a seller with zero equity or an overpriced property willing to walk away from their home without any regards to foreclosure and ruining their credit.
sub 2 is way of getting into a property - potentially a free house without any bank qualifications, credit checks, down payments, closing costs, no commissions.
sub 2 usually involves getting a quit claim deed from the seller to get control of ownership but is normally frowned upon and has its liabilities. youll see savy investors using title holding land trusts as a vehicle to control a property via sub 2 then using fix/flip or seller financing as the exit strategy.
sub 2 disadvantages are violating due on sale clause, tax reassessments, seller is still at risk with their name being on the loan, seller typically has no control, ruining credit and potential foreclosure if the incoming buyer/investor no longer makes payments.