There is actually no harm but it will be very annoying because you will always receive notifications coming from the airdrops you've signed in. If you don't want that to happen, create an alternative email address that is only intended for airdrop and any other bounties. In additiion, it is not recommended to fill those forms with your true credential it may be a subjective for account selling if you signed up on a wrong form or a scam project.

If you are pertaining to ERC20 tokens or any other ALTCOINS.
Always be updated in telegram channels. Look for Airdrop and Bounty Signature in Marketplace Thread. This is a good starting point to have some capital for trading. But there are things to consider before joining any of these:
1. Rank up keep posting with relevant and juicy post to gain merits. Look for Meta, I think TMAN has some challenge for us beginners.
2. After you reach Member you can now join any of the Airdrop and some of the Signature Campaigns. Also joining Bounty in exchange for some ERC20 TOKENS can be helpful.
3. If you have now token. Wait for them to have a value and start trading. But be careful cause there is a higher chance of losing money if you dont have any knowledge about this very volatile market.

Hmm you can find services that paid Altcoin at Altcoin Marketplace but you need to be at least Member.
https://bitcointalk.org/index.php?board=161.0
It might help.

Even these two accounts are farming merits to each other, why bother, even if they collect a huge amount of post it is pointless, unless they can spread theirs to help other members in this to reach a higher rank.

Cool, can you help me out?
How can I join your program? As of now my post count is 1
I will repost my post count. Check me out.

There is nothing to be afraid using google authenticator.
Pros:
You can have extra security in your exchange account. Either it is gmail, facebook, faucets as well as wallets.
Cons:
If you lose you phone or you forget you google authenticator codes, you will lose acces in any of your account.