Sometimes they are not necessary and an easy change of variation for lets say a bridge part works better then a fill...

But in songs where the whole sounds kind of uses the same backing, using fills at the right moments works well to make things a lot more sparkling,,

Next to fills and breaks and variations, there are also the multipads to make a performance more dynamic, which is another way of realtime arranging....

And lastly on the Genos, there is the live arpeggiator for the right hand, which also can be used to weave in with the rest of the arrangement..


Which leaves me to conclude that fills and breaks are certainly very important, but not the only way tonarrange on an arranger key...