Hiring a full-time professional is always going to be an added responsibility for a company because of the fact that as an employer you need to take care of every requirement (salary slips, payrolls, fringe benefits, and insurance coverage) every month.
On the other hand, if you outsource a professional from any firm to do the bookkeeping, you are giving the entire responsibility to a firm. And, the firm is going to ensure that they deliver a flawless bookkeeping at the end.