Depends on the platform. Facebook and Youtube monetize very well. Then there are platforms that lumber on marginally for years like Reddit and Twitter, or where the commercial pressures of advertising are particularly obnoxious. (I think of that band Jefferson Starship which never made up its mind if it wanted to be commercially successful or have artistic integrity.)

On the other hand there are sites like Danbooru which seem to thrive without advertising probably because the nature of their content drives advertising away.