Photoshop can re-scale images better than most programs.So there are exceptions where I'd prefer to re-scale them myself.
There are a number of factors affecting a PowerPoint presentation.
PowerPoint can create a misleading representation/canvas view of what you're actually doing/producing in the long run.
A Slide is scaled to 1280 x 720 by default. In the editor.
Yet, the default slide is actually 13.333 X 7.5 inches. This
is the equivalent of a 4000 X 2250 pixel image. So the slide is actually much
larger than what you see at 100% scale.
If you export the images you’ve imported and placed in that slide. PowerPoint exports them at 1280 x 720 by default. Which reduces the sharpness of larger images. The larger the image, the greater the degradation.
Yet, if you record a slide show. The monitors resolution, dictates what resolution the image appears at. It’s resized to fit the monitor. So a higher resolution monitor can display/record/produce a higher quality image.
If you look at the image below. There are 2 separate screen shots of a recording in progress. The top one is being recorded on a 1280 x 720 monitor. The lower one is recording at 2560 x 1440. If you click on that image and view it at 100% Scale. You will see the lower image is sharper and more detailed than the top one. Yet the PowerPoint settings are identical.
If you were to record that same presentation on a 4K monitor. Which is 3840 x 2160 pixels. The image would look better yet. As it would be scaled closer to 100% of its native resolution.
So the workflow can/will dictate finial output quality. You need to consider these factors when creating a presentation.
I’m not a PowerPoint user. So I may be overlooking something?
However, the resolution of your Images, Video Dimensions/Slide dimensions, and other factors are all relative. So I feel my information is sound. If I’m incorrect, I welcome any corrections others can offer.