Service Level Agreements (SLAs) are pretty common when services are being purchased, we all expect that our business grade ISP, cloud providers, etc will offer a guarantee of 99.9% uptime, X amount of bandwidth, et al...
My question however is, is it common to have a similar written, contractual obligation within a company such that the IT department provides an SLA, not necessarily to the employees but to the other business units.
There are obviously other factors that include size of the company and the IT department, the company structure as some companies IT actually bills the other departments for service, and many more, but as a broad generality is this something that "most" companies would or would not do?