If hiring an accountant or lawyer does not result in additional payroll costs why would a company want to hire an accountant or lawyer on staff full-time?

If hiring contract workers does not result in extra payroll costs, why would a business employ workers as opposed to hiring contract workers?

If you were taking out a loan from the bank, would you select a secured loan that had a lower interest rate or an unsecured loan with a higher interest rate? Why does the collateral impact the loan interest rate?