That's my understanding of it, too: It indexes media files so that you don't have to. Really quite redundant, since the system is already designed in a way that encourages organization (with clearly named folders on the user's home that every Maemo-targeted program knows to work with, and file transfer tools having shortcuts to choose those folders).

Personally, I ran apt-get remove metalayer-crawler and never saw it again. Note that this seems to permanently kill the thing; trying to reinstall results in apt complaing that it cannot find the package.

Having said that, it would probably be more useful if everything else (eg: Canola, the file browser) used its database. As is, I couldn't justify having it run, given that the things using it are so few.