If you are working with raw images, then Photoshop must create a new copy of the image and return that copy to Lightroom. Neither Photoshop nor the Nik tools have the capability to edit raw image data. So the image is converted during the transfer from Lightroom to these other programs, and this requires the creation of the new image when you finish your editing.
When I work with raw images and know that I'm going to be using the Nik plug-ins Or Photoshop, I will do as much as I can to the image in Lightroom before I call those other programs because I know the extra file is going to be created. After that file is created I will do work with other plug-ins or Photoshop without making any adjustments in Lightroom, and choose to edit the original. That way no additional copies have to be made. Then, when I'm certain that I just need to make final adjustments, I will finish the processing using Lightroom.
If you are working with non-raw images then Lightroom should give you the choice of editing the original or editing a copy with Lightroom adjustments. My suggestion is to always do your work with the Nik tools and other tools before you make any adjustments in Lightroom. Then you can choose to edit the original rather than create a new copy if it is a TIF, JPEG or PSD file. If you are working with a raw file then it will be necessary for the additional file to be created. But use all of your extra tools first before doing any Lightroom adjustments. That will help you cut down on the number of copies that are created.
One can make repeated round-trips between Lightroom and an external editor (for example, Photoshop) without generating any additional versions in the LR library.
that is, besides the initial one: Lightroom must create something OTHER THAN the initially imported file, since the ethos of LR is that only THAT would be appropriate to be physically altered: the originally imported file being regarded as sacrosanct. So creating a new version (Edit a Copy with LR Adjustments) is the default when you Ctrl+E or Command+E on a Raw.
However once that new file is made and externally edited, and the results returned to LR, any further updates to this external editing get automatically noticed and then displayed by LR. That is regardless how that file has been accessed by the external editing program: either directly from the file system, or else using LR as your front end to locate the image, and request another external editing session with it. This option (Edit Original) is the default when you Ctrl+E or Command+E with a TIFF or PSD.
If using a non-Adobe utility, it may be worth looking into options to use that in PS plugin form hosted within Photoshop, as opposed to via a standalone utility / LR plugin interface... since the latter may presume that you will always want to invoke the creation of a fresh file and of a new separate LR version to correspond with that.
Furthermore, by using Smart Object editing, your 3rd party processing utility (such as Nik) may be able to apply nondestructively (can be re-adjusted repeatedly) over the top of a base Raw conversion, which itself also retains the ability to be reconsidered in the future. Also any layer based PS editing can share in the same physical file and in the same LR version too. All represented as a single TIFF (or PSD) back in LR, alongside the Raw file that it originally came from, and which is still encapsulated within it.
My experience has been that Lightroom will not allow you to call Photoshop or other plug-ins when referencing a smart preview. If you know something different I would be interested in hearing from you. But my understanding is that the smart preview is not the original image, and there would be no way to apply Photoshop or Nik adjustments from the smart preview to the original file.
I was not referring to Smart Previews in LR, but to the Smart Object workflow between Lightroom and Photoshop.
Richard & Jim
Thank you both for the response and information definitely helped.
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