Google Photos has long provided one of the best deals in photo storage: it will back up your entire library for free, as long as the images can be compressed slightly. However, as of tomorrow, June 1st, that deal is no longer available, and you are now consuming Google storage (which you may have to pay for) whether your images are compressed or not.
When it came to photos, the compressed and uncompressed versions were frequently indistinguishable. However, once you start losing resolution, the compression really begins to show.
As long as the original file is less than 16 megapixels, the result can be barely distinguishable. However, for videos, there is no doubt that uncompressed is the way to go. It's a shame Google doesn't allow you to set different options for photos and videos.
The real disadvantage is that compressing your photos does not always save a significant amount of space. As you upload thousands of new photos to the cloud each year, that extra space quickly adds up. However, if you're going to have to pay anyway, it might be worth it to keep your photos — and especially your videos — at their original resolution, especially if you're uploading them in higher resolutions.