They would both require licenses.
You would want them to both be configured exactly the same way.
Then you would develop your apps on the DEV server and after testing and QA you would then export them out and import them to the Prod server and publish there. Users would most likely only have access to the Prod server.
Also the Production server can be kept stable and only have things tested as ok applied to it.
The most important component is Qlik Sense itself, which could be tested on Dev first and not applied to Prod until one has full confidence in it.
The classic set up is to have 3 environments, Dev, Test & Prod. But for smaller places with less money Dev & Test are often merged onto a single environment.