A quick piece of information that I got confirmed by Marketo Support that I thought is worth sharing:

 

When you add leads to your 'Marketing Suspended' List, these leads will be not receive Marketo Emails but emails from Salesforce can be sent out.

 

Be mindful that suspending doesn't mean unsubscribing.

 

Image result for suspended

 

 

You can create your own rules to suspend leads.