“When is one recommended insulin injections?”

If you are on optimal/full doses of several oral medications and such levels are still above goal, we generally proceed to insulin therapy or other injectable options (that are not insulin, for type 2 diabetes) in addition to some oral options.

Usually when the Hemoglobin A1c is too high (>9.0%) and the diabetes is not in good control despite oral medications.

Type 2 diabetes is a metabolic state of high blood glucose mostly caused by insulin Resistance and relative insulin insufficiency. Unlike type 1 diabetes (absolute insulin deficiency), it may take long time to evolve into full blown symptomatic diabetes. The initial treatment is diet, exercise, and weight loss. If blood sugars are not normal, then oral medications are introduced; insulin sensitizers, mainly Metformin, are started. If blood sugar is not controlled (HA1c <7.0), then a 2nd, 3rd, etc., oral medications with a different mechanism of action is also introduced depending on the individual response. If blood sugars are not controlled with all these medications and HA1c stays above 8%, then long-acting insulin is introduced besides the oral medications. If HA1c stays above 8%, then meal times short-acting insulin are required and adjusted to bring the blood glucose to a desired goal between 70-140 mg/dl (HA1c <7%). If blood sugars on oral medications are above the desired range, then insulin should be introduced, at least long-acting insulin either daily or twice a day depending on the individuals situation. In case of abnormal kidney function, oral medications should be lowered or stopped. In this scenario, insulin is the way to go. High blood pressure and abnormal lipids should be aggressively treated. Also, any diabetic patient with HA1c of >7% persistently should consider treatment with statins (cholesterol medications) to protect the heart regardless of there cholesterol level in the blood.
Remember, medicine is an art. Doctors may practice medicine slightly different regardless of guidelines or evidence based medicine. So, expect some differences among practitioners. This should not be seen as bad or good. Just normal variations. This is general advice but does not substitute your doctor's advice. Please discuss it with your doctor as well.
Good luck.

That is a difficult question. Some people with T2DM never need insulin and some need it very early in the course of their disease. It depends on the severity of the damage to the insulin producing cells of the pancreas. If they have been badly effected by whatever causes the disease (genetics, overweight, insulin resistance, factors we don't yet know, etc.) then we may start insulin soon. Most people with T2DM have some residual insulin producing ability so may stay on oral agents for a long time. Multiple oral agents at once & a variety of agents (there are about 20 now) should be tried along with diet, exercise & wt. loss (life style change). Check blood sugars regularly along with A1c and adjust meds. When a combination of 2 or 3 oral meds will not control the BS & A1c then is the time to start insulin injections. If only the fasting BS is up then we continue the oral agents and start a once a day long acting or basal insulin to control things during the night. If then BS after meals is found to be up we would add insulin at mealtimes while continuing the basal insulin. Some of the oral agent may then be stopped but we like to continue metformin for some effects perhaps unrelated to diabetes. We might also continue or start a GLP1 RA injection as this will help the insulin and may help weight loss. There is some evidence that it may halt or slow death of the insulin producing cells & may even cause some regeneration of these cells. The above are not proven yet but some animal data are hopeful. By the way, a need to go to insulin does not mean you have done anything wrong. Degeneration of the cells is a part of aging that diabetes accelerates. But you should follow good health practices to prevent insulin resistance & keep a load off the cells to help preserve them.
Good luck!