As my Maven project grows, I'm trying to stay on top of the project structure. So far, I have a nested directory layout with 2-3 levels, where there's a POM on each level with module entries corresponding to the directories at that level. POM inheritance (parent property) does not necessarily follow this, and is not relevant for the purpose of this question.

Now, while the nested structure seems pretty natural to Maven, and it's nice and clean as long as you are on one particular level, I'm starting to get confused by what I look at in my IDE (Eclipse and IntelliJ IDEA).

I had a look at the Apache Felix sources, and they have a pretty complex project in what seems to be a flat directory structure, so I'm wondering if this would be a better way to go.

What are some pros and cons for either approach that you have experienced in practice?

Note that this question (which I found meanwhile) seems to be very similar. I'll leave it to the community to decide whether this should be closed as a duplicate.