It depends on the job. On most of the sort of work we receive, it'll take me all of a couple minutes to drop the PDF into InDy and add bleed there. Re-export from InDy and you're good to go.
(For example: maybe delete the background in existing PDF and replace in InDy with bleed; maybe there's a photo bleeding off - you can delete the photo from the PDF, after having saved it somewhere else, then drop into InDesign and resize.)
It is a versatile, sometimes round-about way to do things, perhaps not sophisticated enough for some people's tastes, but for simple jobs is quick and reliable.