Indexing a file needs to be done only once, and when it changes.

Yeah, after dumping my music collection on the N9, it was busy for a few minutes indexing. And indeed, after syncing all my e-mail to my desktop even its 3.4GHz core i7 had its work cut out for quite some minutes. (on the N9 no such problem, as only the last month or so is synced) That would suck if that sucks the last bit of juice out of the battery. But indexing lots of files can be done when charging, e.g. when high power drain is much less of an issue if any at all.

To me the upsides are well worth the downsides.