I've actually created a visual aid to understand the reasoning and explained it here:
https://loopedback.com/2017/05/15/eigrp-how-eigrp-forms-relationships-over-different-types-of-wans-we-are-getting-close-to-done-with-eigrp-review/
It's so Service Providers can keep routing instances separate for customers with overlapping subnets, and the same with VRF-Lite, only obviously on a smaller scale if you have a couple sites with overlapping subnets, its simply designed to keep routing instances separate.
