In my opinion, you have bought LrC so that its Catalog can serve as the front-end to an image library. So it is the Catalog that you would already be using to find / organise and thus to view the image that you are considering editing in PS. So it makes sense to invoke the external edit from that same place, and by doing it this way you then get the results of your editing reimported back to the Catalog and presented alongside the starting image. You can then do further stuff inside the Catalog using that new image version, including applying further Lightroom edits nondestructively over the top.
There's more: in Lightroom there is not necessarily an exact 1 to 1 correspondence of files, and images. A particular file (for example a camera original file - JPG or Raw - but could equally well be a PS edited version saved to TIFF or PSD) can show as multiple thumbnails, each one independently adjustable and croppable and organisable using Lightroom's own tools. These additional versions referring to the same file in common, are called Virtual Copies. And any of those can be sent out to PS for further work if you want, if you do that from inside the Catalog. These additional virtual copies have no existence outside of the Catalog though, therefore there is nothing there that it would even be possible to open into Photoshop directly. Lightroom must be involved. I
t may sound perhaps counter-intuitive, but in practice this sort of thing is IMO what's great about the Catalog system. Tasks can be (at least to some degree) un-tethered from usual physical limitations, when they are carried out in a more virtual way. And that allows you to just work visually based on what you see, rather then getting involved in lots of technical steps.
So, see an image inside LrC, send a copy of it out to PS, Save and close PS when you are finished and you see the edited image. You did not tell PS where to find the image it opened, you did not set where the new file should be saved or what it should be called, you did not tell LrC to import the result and where to find that. And if one image is Raw based and the other is PSD based you can just operate on them and do stuff with them just the same, including making virtual variants for one or another purpose (maybe cropped differently, or adjusted differently., or grouped together in a virtual Collection).
... View more