Lightning Process Builder and Process Builder are the same tool. Process Builder is a way of automating business processes. In other words, it is the upgraded version of the Workflow Rule. Whenever you create a process, the system automatically creates a Flow and a Flow Trigger to call this Flow. This happens behind the scenes, and the user doesn't need to interact with these shadow Flows. The Workflow Rule has several limitations. It doesn't allow you to update child records. Also, it doesn't allow you to Post to Chatter, create a child record on a specific action, or automatically submit a record for approval. To overcome these limitations, Salesforce introduced Process Builder in the Spring '15 release. There are a few advantages of Process Builder, which are as follows:

• It allows you to create a complete process in a single screen, unlike Workflow Rules, where you have to move from screen to screen to create a complete rule
• Its visual layouts allow you to create a complete process using point-and-click
• It helps you minimize Apex code usage
• It allows you to call Apex from Process Builder, where Apex is still required
• It also allows you to create multiple scheduled actions for the criteria from Process Builder
• You can easily reorder the process criteria in your process with drag and drop
• It is also possible to execute multiple criteria of a process 

As of the Summer'17 release, Process Builder runs in the system mode so the object and field level permissions will both be ignored for the user who triggers the process. Visual Workflow runs in the user mode, which means that at runtime, the user who triggers the Flow, their access on the object, and field the level will be counted. However, if a process launching a Flow, the whole automation will run in the system mode. Let's take an example if you are trying to update the Opportunity Next Step field:

1. If you use Process Builder to achieve it: If the running user doesn't have access to the Next Step field, Process Builder will be able to update it.

2. If you use Flow (custom button to call a Flow): If the running user doesn't have access to the Next Step field, they will get an error.

3. If you use Flow to achieve the same thing and you are using the Process Builder to auto launch the Flow: If the running user doesn't have access to the Next Step field, then too Flow will be able to update it.

If any of the actions fail at runtime, the entire transaction will fail and an error message will be displayed. There are some exceptions or settings around it, which we will discuss later in Chapter 8, Enabling Flows to Work with Lightning Experience.