Snaps are ways to ship software where everything is bundled together and the developer doesn't need to sort out dependencies on the distribution. This often makes the package bloated. It has no direct benefits for users, but it makes life easier for developers. Thus, indirectly, users might get access to some software they would otherwise need to compile if no one's got it readily available for the user's distribution. Ubuntu appears mostly to be using it because they don't want to bother sorting out dependcies. On Ubuntu, and only on Ubuntu as fast as I know, some packages in apt will install the snap version silently, which, I think rightfully, annoys a lot of users.

There are similar alternatives, like flatpak, which also bundle dependencies. Some aspects of snap are proprietary to Canonical, the makers of Ubuntu, so you'll find people who are ok with the somewhat bloated software if it makes software more widely available, but aren't happy with a proprietary format in what is largely an open community.