I am scanning photos for a friend. They'll require some minor touchup like cropping, color adjustment that I plan to do in lightroom. When I am done I will give her the photos. I have no intention of keeping a copy. I am thinking a separate catalog makes sense in this case. I don't want to overload my catalog with all this data I don't plan to keep. Appreciate any advice and experience you could share.
Yes, it makes sense to use a separate catalog. Do remember that you will have to export the images in order to apply the edits. Or -if your friend uses Lightroom Classic too- send her the catalog as well.
I have done scanning jobs of a large group of images a couple of times for friends (to create a montage and slide show for a funeral) and find the simplest way is to import the images directly into my main catalog, all in one folder. Then I do the necessary edits, export the images, and deliver the images either on a thumb drive or uploaded to my Shootproof site. Some time later, when I'm sure they've received the edited images, I can delete them, then the folder from LR, which will have the effect of removing them from my hard drive as well.
By the way, if you haven't already discovered this trick, lay as many prints as you can fit onto your scanner at a time. Don't worry if they're not all in the same orientation. Then create virtual copies in LR, one for each discrete image in the scan, rotate, crop and edit as required. Scanners are slow, and this saves a ton of time!
I also agree, as an archive you will not regularly use or visit, a separate catalog is fine. Otherwise I'm all for just one catalog. FWIW, I've done a similar task for friends and just spun off a separate catalog and backed it up to the cloud for them.
Author “Color Management for Photographers" & "Photoshop CC Color Management"