Explanation
Permission sets are used to grant additional access to users based on their functional or departmental needs.
Role hierarchy is used to grant access to records based on the user's position in the organization. Individual profiles are used to define the baseline access for users based on their license type and job function.

Explanation
Contacts to multiple accounts is a feature that allows a contact to be related to more than one account. This is useful for scenarios where a contact works at multiple companies or has different roles at different accounts.
Creating two contact records would result in duplicate data and confusion. Merging the two account records would not solve the problem of relating the contact to two accounts.