Goto definitions, intelligent autocomplete, inline diagnostics, smart renamers, type hints and more are all available.
All with very little configuration and it works the same no matter the language (as long as it as SLP support).
For example: in VSCode you can select/hover over any expression and it’ll tell you the computed TypeScript type. None of the current language server tools for Vim (eg ALE) give you that information [0]. Why would I live without this useful feature just to use Vim? I love Vim, but I love knowing the type the TS compiler thinks an expression is even more, especially when good enough Vim emulation is available.
You can define your own popup(:h bexpr) however you feel, including per-filetype or buffer. Instead of simply operating on the variables it defines to you can also work upon the selection by querying the register(:h quotestar) instead.
As an example, I like displaying wordnet¹ popups when writing prose. Occasionally, I'll also dump diction² output in to a popup too.
However, I do think that using messages(:h :messages) might make more sense for selection info in general. That way you can select a text, call a map to display information, and still easily recall that data when you're in another place via :messages at a later time. Depends entirely on your use case, and once again how interested in writing the functionality you are.