Modality is easier to create because it lets you write more batch-processing style code and less "synchronize all widgets on every change" code. The latter can

Modality is easier to create because it lets you write more batch-processing style code and less "synchronize all widgets on every change" code. The latter can massively increase the scope of performance tuning if a lot of processing is involved to do synchronizations. Hence if the UI is in a "supporting" role(e.g. an internal tool) rather than the core of the product, going modal at key points may be appropriate for a version 1. You can always iterate on it.