Injected basal gives a fairly consistent amount of background insulin all throughout the day and night. Some people need significantly more or less basal insulin at different times of the day. Injected basal insulin can't be adjusted to suit these times but with a pump you can make these adjustments. For example my daughter needs more basal insulin from about 5am until about 10am, then she needs considerably less basal insulin between 2pm and 5pm. With the pump we can programme it to change basal rates to cover these needs, with injected insulin we could not adjust it for specific times of the day.
With bolus insulin we can deliver insulin all at once, or we can deliver part of it now and the other part over a period of time, or we can choose to deliver all of it over a period of time. This gives a lot of flexibility to precisely match insulin delivery to the profile of certain food types like pasta, pizza and high fat foods.
For exercise the pump also gives a lot more flexibility. If my daughter has a very active day I can adjust the basal insulin for however long I feel necessary to avoid hypos several hours after exercise. I can also choose to reduce the basal insulin an hour or two before exercise to avoid hypos during exercise.
During sickness the basal insulin can be adjusted higher to avoid high readings due to infection. This works more effectively than correcting with bolus insulin after readings have already risen. Because the basal insulin is a rapid acting insulin and it's infused minute by minute if the temporary increase in basal needs to be cancelled it can be done immediately. An increase in injected basal insulin will remain effective for the next 12 to 24 hours so if that increase is no longer needed you're left with low readings and possibly hypos until it's effects wear off.
I'm sure there are other benefits that I could think of but these are the first few that spring to mind which we have found useful. Of course there are disadvantages too with pumping but for us the benefits far outweigh them.
