If you are talking about photography post processing (be it in a camera club or online) then it is inevitable that you will be part of a debate about whether you should use Photoshop or Lightroom. As there is no simple answer don’t be surprised if things get heated.
The flaw in these debates is that Photoshop and Lightroom are not alternatives for each other. While Photoshop is a massively powerful image editor, you don’t use it to manage your photo library. On the other side while Lightroom has a great library module and gives many adjustment options, it is not an image editor.
So Photoshop and Lightroom and not alternatives, they complement each other and that shows through in how they integrate together. If you need to do something that is beyond the adjustments built into Lightroom then you can take the image out to Photoshop (or other program) and then bring it back to Lightroom for exporting or printing.
Keeping within the realm of Adobe products, instead of comparing Lightroom to Photoshop, the valid comparison is Lightroom against the combination of Bridge and Camera Raw.
So what is the harm in arguing over Lightroom or Photoshop? Apart from the time that is wasted, it can also provide incomplete information to the inexperienced photographer. This may have a greater negative impact in the long run.
What do I mean? Well, at the camera club we want to encourage beginners to be out there taking photos and submitting them in our monthly competitions with the critique feeding back into better photos in the future. To me this includes talking about concepts and effects, not the specific steps in a particular tool.
I have seen an experienced photographer demonstrate to a beginner how to add a vignette to a photo via a complex series of steps (selection, feathering, new layer, fill, opacity blending, etc) in Photoshop. The same vignette could be added in Lightroom (or Camera Raw) by moving a slider which means that the beginner could take in more about why to use a vignette than how to apply it.
My view is that a beginner should start with Lightroom to manage their photos and apply adjustments. It is only once they are much more experienced and are pushing the limits of the Lightroom adjustments that they should consider Photoshop. And don’t forget that taking the right photo in the first place is better than fiddling with post-processing.