I'm not sure what others do but since I've had Diabetes since 1961, I've needed to find more real estate through the years. About 11 years ago, I had depressions(Lipoatrophy)in my arms and lower tummy. I had been using Lispro by injection for 6 years before this happened. My arms and lower tummy were my favourite spots.
While reading up on this subject years ago, I noticed that the reports were that since the new Insulins were being used there were hardly any new cases to report. Perhaps true because many of the Endos and GPs were not checking Patients for Lipoatrophy. Also some Patients probably didn't mention the dents to their Endos or GPs because they were afraid to or didn't realize that these dents could be related to Diabetes.
Anyhowsie, that's why I experimented with more and more new injection sites. I was told to rotate injection sites when I was a Child but no one told me why(I hate when they do that). I was one to follow orders, not ask questions.
The diagram that Jag1 posted is more realistic as in areas to give injections/infusions. I actually give injections in more places than what are on the diagram. I give them in my shoulders, higher and lower in the front and side thighs, up to my rib cage(not boobs). I have severe RA thus I cannot do any back areas, so my Hubby gives me injections in most areas of my butt, in the back of my thighs(not the calves-OUCH), many areas on my back. I take an injection in muscle especially when I want to bring my BG down faster. I find different muscles lower my BG faster and some not as fast. I have used Prednisone daily for the last 9 years(off and on before that), so I need to be inventive to keep my glucose levels in a good or reasonable area.
I was 107 pounds last year until my Rheumy took me off of the MTX and Rituxan. I am grateful to be back to my normal weight(126 pounds). I have been doing this for about 10 years and I have not any muscle damage, dents and have had no hypos due to muscle injections, so far. There may come a time, who knows. I have been careful to monitor, rotate sites and I don't do "marathons"(as if, :-) ) when I'm injecting into the muscle. I am careful to do less or no exercise at that time except for normal walking at home, etc.
Oh, and many of my muscles did hurt in the beginning but not as bad now since I'm used to it. I take a deep breath. RA is waaaay more painful. We all have to do what we need to do to treat our Diabetes in a way that suits each of us best. This is one of my ways.