In Pharo, it's usual to run code inside Playground, and using Transcript to print the output. But I noticed it's also possible to run code inside Transcript, not only printing things there. For example, if I type:
Transcript clear.
Inside the Transcript window, and run it by Ctrl+D, the window will be cleared. So my question is, when does make sense to run code inside the Transcript window instead of Playground? Is there a use case?
To answer your question, we need to clear some things out:
You can run any code (almost) anywhere in the image. So if you open a method for example, type somewhere there Transcript clear, select it and hit Ctrl+D the transcript window will be cleared.
Transcript is just a "singleton" linked to a window that makes it easy to output some text and see it somewhere. It's not hard to construct a similar functionality on your own, or you can even output to a file for example. Transcript is there just for convenience during a troubleshooting activity. I would still recommend to use the debugger in a first place, but there may be situations where a debugger won't cut it.
Playground is a tool designed to "play" with your code. It's paired with an inspector, so whenever you run some code, you can inspect the resulting object in a user-friendly way. There are also some other features, like browsing variable bindings or storing code snippets, or browsing the playground code history. As I mentioned before you can run any code anywhere, but Playground is optimized for trying out stuff.