A lot of apps use it, so yea, unless we want many (most?) of the apps to no longer work, we need it.

Don't even think about removing it using ADB, it's a very important part of the system, the other day Google released a faulty update that broke many Android mobile apps and some Android TV ones, though that doesn't mean you shouldn't keep it up to date.

Let me explain what it does, in the most basic terms. The system webview is pretty much a "browser" component, which can be used by any app that needs it, internally. The most obvious example of such a use would be those mini browsers, apps often have in them, displayed when an app opens a web link without launching an actual browser for you. Thats just the system webview inside that app, pointed to the link in question. But thats far from the only thing system webview is used for. Many modern apps frameworks are basically a little website, running on your device (well, not exactly, but close enough), and they actually use system webview as their main interface component. For an app like that, disabling the system webview would equal pulling the plug on it's ability to render either a big part of, or it's entire user interface, completely breaking this type of app.

It won't insta-kill your device if you disable it, and most likely you'll be able to reenable it without long lasting damage, but thats not something you just disable cause you happened to think its bloatware, want to save a few mbytes of space, or something like that.

Hope this provides a somewhat better explanation.

I suspect our Android TV (Google TV) Home screen uses it

More than you need your brain from what it looks like.