Access Token contains almost all information from Identity Token - oauth-2.0

Question

The tokens below are returned upon initial token request with Azure AD B2C. access_token contains most information that id_token contains.
My questions are that:
1 Since access_token contains most information that id_token contains, what scenario can access_token be used in place of id_token? what scenario must id_token be used instead of access_token?
2 What are the rules regarding use of both access_token and id_token in general?
Result upon initial token request
{
"access_token": "access_token",
"token_type": "Bearer",
"expires_in": "3600",
"refresh_token": "refresh_token",
"id_token": "id_token"
}
Below is the decoded token for the respective token:
Please note that access_token contains most information from id_token, including user information.
access_token
{
"iss": "url",
"exp": 1550539339,
"nbf": 1550535739,
"aud": "audience ",
"idp": "LocalAccount",
"sub": "guid",
"name": "user#email.com",
"emails": [
"user#email.com"
],
"tfp": "B2C_1_ROPC_Auth",
"ver": "1.0",
"iat": 1550535739,
"azp": "guid"
}
id_token
{
"iss": "url",
"exp": 1550539339,
"nbf": 1550535739,
"aud": "audience ",
"idp": "LocalAccount",
"sub": "guid",
"name": "user#email.com",
"emails": [
"user#email.com"
],
"tfp": "B2C_1_ROPC_Auth",
"ver": "1.0",
"iat": 1550535739,
"auth_time": 1550535739,
"at_hash": "access_token hash"
}
Update
Further to question 1 above:
Since access_token contains most information that id_token contains, can access_token be used instead of id_token? That is, when id_token must be used instead of access_token?

Answer 1

I will take google as a example,
1) let say you want to implement social login where u mostly need fields like email, 'first_name', 'last_name'., these fields are mostly available in id_token. so id_token is perfect suitable for authentication.
2) later u need to fetch google contacts of the login user., In such scenarios u can't get contacts of the user in id_token. this is where access_token comes, though u won't have the contacts in access_token but all permission to fetch the contacts.

Answer 2

An ID token is intended for authentication. It is represented as a JSON Web Token (JWT) that contains claims about an authentication event including the identity information for a resource owner. The ID token is intended for a client application (a single-page app) and its aud (audience) claim contains the OAuth 2.0 client_id of the client application.
An access token is intended for access by clients to resources that are owned by a resource owner. It is represented as either a JWT (e.g. Azure AD B2C represents an access token as a JWT) or an opaque token. The access token is intended for a resource application (e.g. an API app) and its aud claim contains the OAuth 2.0 client_id of the resource application.