The only time I found a dev instance in addition to a stage instance useful was for a major rework like a complete redesign and/ or restructuring part of a relaunch where you touch everything. This usually means dev of a few months where you still need to perform maintenance and content/asset updates on your production community via the stage instance.
Other than that I only ever used a dev instance as a playground to break stuff, but for the exact reasons Stan described it was to cumbersome to incorporate into a multi-instance development workflow.
Curious to learn why you asked to get one in the first place, CarolineS ?