Contact to Multiple Accounts lets sales reps relate a single contact record to multiple accounts so that they can easily track the relationships between people and businesses.
Instead of creating new functionality layered on top of existing features, Salesforce decluttered first; they threw out the old ‘Account Contact Roles’ feature, and made way for ‘Account Contact Relationships’.
‘Account Contact Relationships’ achieves the same thing as the retired ‘Account Contact Roles’ feature, so you should absolutely use this if you want to simply define a ‘role’. However, what ‘Account Contact Relationships’ can do in addition to the retired ‘Account Contact Roles’ is create a role for a contact on multiple accounts.
For more information please visit: Salesforce's help article HERE