Hi we have been using MC for a while, but not connected to SFDC. We are currently use email as subscribers key.
I understand that tracking info will not come to SFDC if we don't use Contact/Lead ID as subscriber key. If we keep using email as subscriber key, are there any merits to connect 2 clouds?
Not really, as Marketing Cloud Connect will only recognize subscribers that use the Contact/Lead ID as actual subscribers. This means any cross-cloud functionality you normally would be able to use isn't available in your scenario.
Though you could use it just to exchange data between clouds, like automating some report-imports to Marketing Cloud and then using SQL queries to populate a new Data Extension that sets the Email attribute as the primary key.
With custom API events you might get some standard features to work, like synchronizing communication preferences by using Microsites or Cloud Pages.
Maybe someone has built a custom SF object-mapping with Data Designer with Email Address as the ContactKey and been able to use it with Journey Builder, but I somehow doubt it..
Anyway, just because you currently use Email Address as Subscriber Key in Marketing Cloud doesn't mean it will always be / have to be like this. Since you are using both Clouds, I would advise checking what else comes with Marketing Cloud Connect.
Apart from being able to transfer tracking back to Sales Cloud, there is a number of other advantages of connecting these two clouds. The main one IMHO is cross cloud capabilities of Journey Builder - where you can trigger a journey in real time, based on changes in records on an object in Sales Cloud. This however also requires Lead/Contact ID as Subscriber Key.
If you keep email address as Subscriber Key, you can however still use a number of AmpScript functions working with Sales Cloud, such as: RetrieveSalesforceObjects, UpdateSingleSalesforceObject, as well as having data from Sales Cloud available in MC as Synchronised Data Sources.
If you want to use the full potential of the integration, and are willing to move your system of record from MC to SC, you can reach out to your Salesforce Account Executive, to discuss the possibility of performing a Subscriber Key migration. This will change Subscriber Key for all your existing Contacts to Contact ID, enabling you to utilise all the above features.
