Norway is a small country, with limited resources and personell..
A battery of MLRS can be compared to a Batallion of M109's..
In that way we have the firepower of a batallion, with 1/4 of the personell required...
The range is also important.
Since we don't have too much artillery, we need to be capable of using the resources we have at a maximum range, and in that way we are capable of reaching a lot more of the battlefield than we could with the same number of M109's..
But this is a bit fftopic: (haha, I really like that smilie...)