Why seaplanes were useful in the Baltic

Were seaplanes ever particularly useful in the Baltic?

Yes. There were few suitable airfields, while small inlets offered comparatively calm water for take-off and landing.

Before suitable airfields became common, Baltic aviation had only a limited number of decent runways to use. Seaplanes could instead operate from the region's many small inlets. Their comparatively calm water provided places where a small aircraft could take off and land with reasonable confidence.