If it's mostly lime, you could soak it in vinegar and not do as much
damage (not that losing the chrome off an aerator that you can't see
anyway matters much).

It does at least two things that I know of:
1) It usually allows you to wash any given item (including hands) just
as effectively with less water (thus saving water). Not sure I can
adequately explain why, but it seems to be the case.
2) It makes the water splash less in the bottom of the sink.

Drawbacks:
1) When you really do need a lot of water to clean something (or have
low pressure), it slows the process.
2) Takes longer to fill a dog dish, pot or water bottle.
3) Eventually gets clogged (but 3 minutes of work every few years will
remedy this).

JMFO