This is an interesting question. The answer is complicated.
If you use injectable insulin and have cells which are still capable of manufacturing insulin these cells may atrophy. Thus, physicians want to keep people on medication that stimulates their own insulin producing cells as long as possible.
On the other hand Lantus, a long acting insulin, in small doses, does not increase insulin levels to the point where natural production is shut down.
Although not truly an "approved" protocol, injectable insulin can be used ocasionally by diabetics who at times must (for social purposes) consume a large meal at a special family gathering for example.
Type 2 diabetics may require an insulin prescription if oral medication and proper nutrition [diet], exercise, and suitable body weight cannot control their glucose [blood sugar] levels adequately.