Please find a copy of canonical answer given by SE Community Manager at MSO below.
From the FAQ of any of the child metas:
Reputation here is entirely derived from the parent website; your reputation is the same as your reputation on the parent website, synchronized hourly. Votes here do not affect your reputation in any way. However, you can earn unique badges here on the meta site.
(Please note that offensive penalties, if levied by the community through spam or offensive votes on your posts here, will affect your reputation on the parent website.)
This has a couple consequences:
- Users have the same powers on the meta site as the parent site. The more someone is vested in the parent site, it stands to reason that that should follow on the meta site.
- Everything drives from the parent site, which is at is should be. The meta site doesn't exist as a place to gain rep.
- You can cast votes more freely based on the content of the post without it affecting rep.
So, you may not be earning the rep that it shows, but it is still an indicator of activity. Don't you want to know when you get an upvote? You just need to think in terms of what each value of rep gain/loss means in terms of vote activity.
You can also earn badges on the meta site that are independent of badges from the parent site. Mortarboard is the first example that comes to mind relating to your rep. Other badges like Good/Great Question/Answer etc relate to upvotes. In the SE system, votes tie to rep. A side effect of it being the same code-base, but I don't see it as a big enough deal that it would warrant changing for the meta sites.
There is also a blog entry that discusses the per-site metas.