Do I have to Create a new email address for each Adwords Account?

The short answer is Yes.

It might sound annoying or pointless to create a new email address for each Adwords account. A friend might ask you to manage their Adwords, do you have to create an enw email, just for them? 

Yes, you have to. 

Because Google do not allow Adwords users to manage more than one account, unless the are an SEM agency (or a 3rd party professional). In that case, you will have to create the MCC. (My Client Center)

Here are some brief points, to avoid any confusion when creating and linking Adwords accounts. 

• You do not give MCC account manager access because MCC is not an account. It is a manager. To link an Adwords account to MCC the invitation has to be send from the MCC itself. And it is not an invitation, it is a linking request done from the MCC dashboard (interface)
• However, both the sub-level account and the Top Level MCC can terminate the access at any time.

• It is not allowed by Google Adwords to let you have access, with your personal email, to other Adwords accounts to administer them, if you already have your own Adwords account. 
• A rule of a thumb: one Email account for each Adwords account. If you want to manage more than one Adwords account, you have to be a 3^rd party SEM Agency, in that case you will need the MCC account (My Client Center), and link the other Adwords accounts (those which each of them has its own email address).

• You do not have to create the email accounts, for the Adwords only purpose, on Gmail. Yet, you can create them on any corporate email, or any email server you have access to.

• Canceling an Adwords account does not authorize you to have access to other Adwords accounts. An Adwords access needs a dedicated email account, or go and have an MCC, but still you will have to create a new email for the granted access, unless you have the customer ID, then you invite the customer with their ID, and they should accept your access.

Conclusion,

If you want to manage multiple Adwords accounts you will need to

1. Create an MCC account.  
2. MCC is only a user interface and API. It is not an adwords account and it does not manage accounts directly.
3. To link adwords accounts to MCC in order to be able to access them directly, you should have the customer ID for the Adwords account (If there is no account, create an email, and an adwords account, and take the customer ID to the MCC to invite this created dedicated account). Or, create the new account on the MCC and create an email account and invite the email account from the MCC directly.
4. The 2 parties should accept and grant access to each other.