I Want to do some rotoscoping work and can shoot some footage at either 1080P or 4k, though the final output will be 1080p. Is there any advantage to working in AE with higher resolution 4k footage? I'm guessing 4k footage is better for green screen work? But what about rotoscoping/key Framing?
You'll have more definition in the edges to help you make a tighter mask, but that means you'll also have more work and the mask bounds will be less forgiving. 4K is more beneficial if you'll be scaling your video layers or if a lot of stabilization needs to be done.
Depends entirely what you want to do with it. Obviously larger resolutions leave more room for "destructive" work like rotoscoping, distortion effects or post-cropping and will be more forgiving of smaller imprecisions that blend with the interpolation when scaling down. On the other hand it will be of course more intense in terms of processing which could be a pain for complex particle effects or dealing with Raw file formats...