Foliage with stationary directional lighting, does that work?

I am working on a small outdoor scene, with some foliage instanced meshes. I started my level with a directional light, set to stationary. However, that leads to very bad shadow quality, even with lighting quality set to “high”:

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But when I set that directional light to “movable”, the shadows look fine:

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I could of course use a movable directional light in my map to get this nice shadows. But that feels a bit much, performance-wise. Is it ok to use a movable directional light as main light source in an outdoor level? If not, how can I get such nice foliage shadows with a stationary light source?

Use stationary directional light with cascaded shadow maps.(instead of per object inset shadows)

That seems to work fine, thanks!