In my case, intellij indexes .o and .dcu, so when I type for example shift-shift and type a file name, it shows only .o and .dcu files. The .pas file are available but only at the bottom of the list. That makes the navigation through file not easy.
I know some folder can be excluded, but that is not really practical. And I didn't see any index filter in intellij (intellij post about filtering files)