SSAS Tabular solution - should we limit it to one model per solution

We have a need for multiple SSAS models, though we have been in practice keeping each model in its own solution. At this time, we have a naming convention across solutions, projects, and models.

I've been asked why we're doing it this way instead of having one solution, with multiple projects for each needed SSAS model. I don't have a good answer to that question, and now he's put a bug in my head.

Since I'm anticipating that this may be a matter of opinion, I'll phrase the question safely: What are the pros and cons of each approach?