Indexing is IO-heavy and does slow things down, that's the nature of it (and Windows is dramatically bad at that), but they have improved quite substantially in

Indexing is IO-heavy and does slow things down, that's the nature of it (and Windows is dramatically bad at that), but they have improved quite substantially in this department recently: whole indexes of large libraries/runtimes can be fetched from the internet so your computer won't be the billionth device to re-index the whole JVM, the IDEs are starting faster, and more features are being made available while indexing in progress (giving less of an impression that "nothing works" when opening a project).