A lot depends on the end product. If you're designing a building, the end product is the building. So at 50%, 50% of your members can be designed. But in our industry, water and wastewater treatment, the end product is a treatment facility. So our submittals are treated differently. For instance, the structural needs to be pretty complete at 50%. We can add details, etc., but the size and shape of walls and members need to be pretty well defined and if they need to be changed, you need to make sure it doesn't affect the process. This is so electrical and mechanical can finalize their equipment based on our backgrounds.
I tend to use that time between the 50% and 100% to do final calculations (I use approximations to size thing up to then), package them up, write specifications and stuff that doesn't affect the physical design, i.e. steel beam connections.