Bigger companies usually have the problem, that it is not possible to write all programs employees want (to save time and to optimize processes) due to a lack of staff and money.
Then hidden programs will be created by some people having (at least some) coding experience (or by cheap students/interns...). Under some circumstances these applications will raise in importance and spread from one user to a whole department.
Then there is the critical point: Who will maintain the application, add new features, ...? And this app is critical. It IS needed. But the intern has left the company. No one knows how it works. You only have a bunch of sources and some sort of documentation.
Does it make sense to try and control or forbid application development done ad-hoc outside of the IT department (with the exception of minor stuff like Excel macros)?