Imagine that you have a wooden workshop. You have a WorkBench and you are building a bird house (Test Plan). Sometimes you need to pull out the saws (Test Script Recorder and Recording Controller) and other tools. You have a tree (record) on the bench that you are not yet sure about your birdhouse. When you leave your wooden store, you don't care that on your WorkBench you only care about the bird house you are working on. When you return, you only want to see a birdhouse and an empty WorkBench. Therefore, after you leave, your housekeeper puts aside the tools and throws out the whole scrap tree that you have on your workbench.
So how to think about it. First of all, this is the place to use your test Script recorder. If you are not using this tool, Workbench probably does not make much sense. When the system I tested performs an update, I sometimes open JMeter Script, I have and write a new record to my WorkBench, and then compare it with what I previously wrote to see if there are any changes in the API calls were made. This keeps everything in order, because the last thing you want is an extra extra challenge in your test plan that you don't need there. Sometimes, when I debug a certain call, I copy the old material to the desktop, just make me guess in terms of testing.