it is best to get a copy of the current one if it is available because it will document the condition of the unit when they first moved in. That way if they damaged the property between when they moved in and when you purchased the property, you will have documentation to make the proper deduction from their security deposit.
I have purchased properties with inherited tenants where the previous owner did not do move in inspections (discounted properties don't usually come from the best landlords). In that situation, doing a new move in inspection when you take ownership is the best you can do to protect yourself from any additional damage prior to them moving on.
This isn't to say all tenants do a ton of damage that requires security deposit deductions. It is not completely uncommon for us to return 100% of the security deposit if the unit is left in the same condition it was recieved. Having the move in inspection is just insurance against a tenant claiming every hole in the wall was "like that when the last landlord rented it to me"