Space-sharing
Cramming two functions into one area at the same time — a desk wedged permanently into a bedroom corner. Weaker than time-sharing, because both functions are always present and so both are always compromised. The thing people mistake for layering.
Two at once = both compromised
A permanent desk in a bedroom makes the room always both and always crowded. True layering removes one function when the other needs the room — time-sharing, not space-sharing.