I see the goal of meditation not so much as alternating between the two modes but rather like balancing them and running them both in parallel.
This entire video is really excellent, but see particularly this bit here, where Iain McGilchrist describes the concept.
The diffused mode could be the broad diffuse attention while focus mode is the the narrowly focused attention. It seems like there is specialized parts in the brain for attention with one hemisphere for narrow and the other for broad. But I think that this is just one theory and it could also be the case that these two modes are more evenly distributed throughout the brain.
For meditation, however, I feel strongly that the goal is to achieve a balanced state of mind, and the balance is as I understand it, is between these two types of attention.