In Dynamics 365 if you want to associate a single Contact with multiple Accounts then we have two options:
- Use Connections
- Create a custom entity
Benefits of using Connections is that it is out of the box, it is fluid means you can add/remove relationships when ever you want. However, from reporting point of view and managing long term several relationships Connections get messy. This is best for temporary setup and if you dont want more features for the Contact-Account relations.
I personally prefer a custom entity because initially Connections suffice the requirement, but as the time passes you would need to capture more and more features/insights of the Contact-Account relationship. The best part of using a custom entity is that you can always extend it, create relationships with other entities, write rules, workflows and business logic. With Connections it becomes difficult to extend it.
Some times you can prefer Connections over a custom entity, that totally depends on the business requirement and level of detail required.
This was my brief insight on whether to use Connections or a Custom entity in Dynamics 365. Hope you like it.
and below article talk very nicely about the limitations of using Connections: