Workflow Rule vs Lightning Process Builder

Workflow Rule - 

Workflow enables you to set up workflow rules that identify what kinds of record changes or additions trigger specified workflow actions, such as sending email alerts and updating record fields.

Workflow have only 4 actions :

Create Task 

Update Field 

Email Alert 

Outbound messages

Lightning Process Builder -

Process Builder can be utilized to automate all workflow actions (with the exception of outbound messages). Traditional workflow can still be utilized in parallel, however, Process Builder gives you the ability to do things that workflow can’t. Although, somewhat of a double edged sword this puts some very powerful tools at the disposal of an experienced administrator. - See more

You can use the Process Builder to perform the more actions as workflow

• It Create a record
• Update any related record
• Use a quick action to create a record, update a record, or log a call
• Launch a flow
• Send an email Post to Chatter Submit for approval
• Call apex methods But, The process builder doesn’t support outbound messages