I think the answer is highly variable depending on the company, the legal infrastructure, that there is no single answer.

My strong suggestion to anyone in this situation is ASK BEFORE YOU DO IT! Your company may or may not have an existing policy. And if there is no policy, make the business case to them. And abide by the decision. A number of employers would be more than happy to save money, especially in smaller companies. However, they have to abide by legal, accounting and financial guidelines ... and more importantly, control policies. What might make sense to an employer on a one-off case might create an adverse incentive for employees to abuse and "game" the system.