An offset loan is a type of lending arrangement, usually for a mortgage, in which a borrower also maintains a savings account with the lender.
That makes offset loans a good idea only for borrowers who normally have large cash balances.
That makes them more attractive to some of the people likely to use them (those with irregular income), but that is not a key defining feature of the loan.
[2] The money in the savings account isn't used to pay back the mortgage and can still be withdrawn at any time.
One way they benefit is by being able to pay off their mortgage sooner or make smaller payments as time goes on.