Fair points all round.

I wouldn't dare advise someone do this work for a for-profit business. They can and must pay for the work.

Generally my view is doing pro-bono for smaller not-for-profits is a good thing. Particularly if they are a local one, helping your immediate community. Things like helping a local charity on improving their donation forms or call to actions on their site. Those are the kind of tasks that a junior can see through to completion that would have large impacts on the orgs they are helping, whilst giving them first hand experience of working with people on projects. These are the kind of organisations and tasks my comments for juniors was more focused on.

With bigger organisations, that can and should change. One thing a lot of people don't realise is that many larger not-for-profits often have budgets for this exact purpose. In saying that, the requirements change rather dramatically as well. I wouldn't suggest Juniors take this kind of work on. It can get pretty specialised.