Hello,
I moved from 2 injections (morning and evening) to 4 injections around 10 years ago. At the time it was a big decision for me as I had good control on 2 injections.
I was put on 4 injections long before I learned to carb count and at the time the main advantage for me was flexibility. I can now greatly vary my meal times and can even skip meals completely if I choose (not that I do that very often, if ever).
On 2 injections (I used Human Mixtard 30 - which is 70% slow and 30% fast mixed together) you had to be pretty strict with your timings to keep your basal covered 24 hours. If you left it too long between them you had a gap with no basal, if you took it too soon you could overlap them. You also had to eat within 30 minutes of taking it. A lot of people would also go high in the afternoon as the morning fast insulin had run out and you didn't inject again until evening. It was very difficult to manage snacks between meals.
On 4 injections the basal/bolus are separate so most people take one injection of basal every 24 hours (some split this into two), and bolus every time they eat - which is where the carb counting comes in as you only need to take enough bolus to cover what you've just eaten.
Personally I much prefer 4 injections now to 2 as I can eat at different times and can manage snacks etc far more easily.
NiVZ