Some additional anecdata: on my maxed out 16” (admittedly Intel) Mac, IntelliJ/PyCharm/Goland/Webstorm are all quicker to start than Spacemacs. I haven’t tried Doom Emacs but don’t get the impression it would be much quicker.
> What does this indexing buy you time wise later?
For simple projects in Python or JS, nothing. For complex projects in most languages, quite a bit. For anything running in the JVM, a whole lot. That's why I pay for my IntelliJ license every year.
The question here is if it's quicker to open a project and be immediately productive in Doom Emacs, and it is, very much so. This is in contrast with Spacemacs, which I used for a couple of years but had to run Emacs as a daemon to make the startup fast.
If I want to go even faster I'll use Vim, but that's mostly out of habit and proficiency.
> And what about starting it with an already indexed project?
Maybe I'm missing something, but it re-starts indexing every time I open the IDE or the project or when switching branches. Is there any other way?
It starts quickly because everything is lazy loaded, if you open project it will start language server, start indexing etc, It's definitely not much faster than IntelliJ, but functionality is still behind.
It does depend a bit on the language server. There are a few language servers that are nicer than the equivalent IntelliJ plugins, though that is generally not even remotely the case for JVM languages that aren't Clojure. AFAICT, the state of the union for Java is that it's not habitable without an IDE, and the only habitable IDE is IntelliJ.