Process Builder:
You can use the Process Builder to perform more actions than with workflow:

1. Create a record
2. Update any related record
3. Use a quick action to create a record, update a record, or log a call
4. Launch a flow
5. Send an email
6. Post to Chatter
7. Submit for approval
8. Call apex methods
9. But the process builder doesn’t support outbound messages.

a. Create a Record, Quick Action uses one DML count.
b. Process can evaluate the same record up to six times in a single save operation.

Workflow:
Workflow does only 4 actions

1. Create Task
2. Field Update
3. Email Alert
4. Outbound Message

a. No DML Limit calculated.
b. May cause your organization to exceed its limit for workflow time triggers per hour.