Trim transparent pixels to to match layer element

If all I needed was a PNG file that was cropped to the visible pixels I would use Composition>Save Frame As>Photoshop Layers, open the PSD, select the appropriate layer and use Image Trim. It not only would be accurate, but it also would not take as much time as duplicating the comp, cropping the region of interest, adding the cropped comp to the Render Cue and exporting a single frame PNG. If you don't want the PSD file then you could select Composition>Save Frame As>Image which would add the whole comp to the Render Cue, then change the output module to render a PNG, then open the PNG in Photoshop and use the trim feature. I think the first option is the most efficient.

No.  You could try and trim your comp, either manually or using the Regio of Interest. 

But it would be easier to just export from AE at the full comp size, then open in Photoshop and use the Trim function and re-save.