When a record has certain values or meets certain criteria

Three of the Salesforce declarative features can handle this use case:

• Workflow rules
• Process Builder
• Visual Workflow
• Apex triggers

In my opinion, I will always try to solve this requirement with workflow rules first, if it can be done within its limitations. If not, I will evaluate whether it can be done with Process Builder and use that to solve the requirement. If there is some specific requirement that cannot be done with Process Builder, I will look at Visual Workflow to solve the requirement. If none of those tools can solve the whole use case, then I will consider using Apex triggers to solve the problem, as a last resort.