I love remote workshops because:
they save a shitload of travel time
the results are already digital and can be easily and quickly shared after the workshop
they are often as efficient and impactful as on-site workshops
But in my experience, here are a few cases where I would rather recommend doing an on-site workshop:
Workshop with participants who aren't digitally savvy should be done on-site.
Some people, regardless of age, aren't comfortable with a computer; a bit of training can help, but in some cases, that's not enough, and it's just simpler to do the workshop on-site.
Workshop with highly emotional elements should be done on-site
When things can get pretty emotional, I recommend doing the workshop on-site because it allows:
Read the full body language of participants: you don't just see a blurry face, but you can see that there is an emotion and can more easily adapt the workshop to the emotion that is experienced.
Use the breaks to sort out stuff: it's always impressive to me how people during breaks fix some of the emotional issues and share key information that then makes it possible during the workshop time to be efficient. In a remote setting, such breaks would be individual and wouldn't allow people to share these emotions and facts outside of the structured exercises.