Approval Workflow: Create Approval Group or Custom Role?

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Hi,

I'm wondering if there's a best practice when it comes to creating an approval group vs. a custom role in workflows? What are the pros and cons of each. 

Also, in terms of maintenance, which one would be more troublesome? For example, for a person that is transferring to a new job, is it hard to maintain when they are in approval groups or if custom roles are created for them?

Any help is appreciated, thank you!!