The one thing I can think of off hand, (and I have never done this in practice) where you would need an instead of trigger is for being able to do updates against views where the view would not normally be updatable.

But except for some truly unusual situations that I have yet to come across in practice, you would be better off either forcing everyone to use a stored procedure to update that information or designing your tables so that you have no need to update the view.

Still, it is an option.