We got one of our largest and definitely most complex customers not long ago. Being rather small, we pushed hard against any customization that we didn't feel was necessary due to business demands, and asked them to follow the way we'd successfully used with our many other customers.

After the went live and the dust had settled, they thanked us and said they were glad we had pushed back. It had forced them to rethink how they worked but the result was much better and more optimized processes.