Because tracking on the client-side gives you can give you a lot more info on what the visitor is doing. For example, if you have a landing page and only track

Because tracking on the client-side gives you can give you a lot more info on what the visitor is doing. For example, if you have a landing page and only track on the server side, you can not know the session length as you only know when the request to that page happened, but not when the user left. I am considering to also add a server-only tracking option for for my analytics platform[0], but the data it provides will be limited by a lot. For example now you can tag users based on the actions they do (click a button, scroll on the page, encounter an error, etc.) and it's gonna be lot harder, if not impossible to track those actions on the server-side, thus user segmentation and other useful features are vastly restricted. Also, as you mentioned, tracking server-side means that your server should be able to run the analytics platform and it might be harder to integrate analytics than simply including a JS on your pages. Imagine you have a static website, hosted for free, in that case you don't even have the option to add analytics on the server-side. [0]: https://usertrack.net/ https://usertrack.net/