Interesting read. Many web applications today rely on client-side rendering, which can perform poorly. Why should users wait several seconds for a page to download, only to wait several more while it renders? In my case, I often have to enable JavaScript and reload the page because I block unknown JavaScript by default.
Another problem is when a web app aggressively probes for information such as installed extensions, as LinkedIn does. That can make the site laggy and practically unusable. But I suppose we could consider that malware anyway.