A design can't be everything. So you have to figure out which things are core and which are not. Some features are core — they are the essential features that the majority of customers need. Others are "edge cases" – peripheral.
The same applies to use cases. Some represent the exact case that the product is made for, others are more eccentric.
Often when teams take feature requests or consider new ideas, they forget to step back and ask whether the idea is core or not. Checking how core it is puts the feature in perspective. Core is about importance, independent of how good the idea is or how well you can implement it (see Impact vs Quality).
It's okay to support peripheral cases or add features that are only valuable to a handful of customers. But they shouldn't interfere with the core, and you shouldn't give up too much Option Value.