I don't aim to use them (unless it's supporting a floating build, like a floating island or aeroplane or helicopter), but if I have to use them because my construction doesn't leave room for actual supports, then I don't care if they're supported by a single invisible 1x2 plate in the corner of a room.
Makes no difference to me if it looks "structurally stable", because even if I did have it all touching without unrendered bricks, the chances are my building is going to look funny anyway.
Does it matter if it's got invisible bricks if I make something top-heavy, or similarly unusual? It wouldn't stand up without them if it was a real building/lego set.