As one co-commenter wrote: it depends strongly on the context. From approx. 5 people up (to hundreds), starting with some whiteboard and constantly keeping up a

As one co-commenter wrote: it depends strongly on the context. From approx. 5 people up (to hundreds), starting with some whiteboard and constantly keeping up a joint documentation can help very much to split work and not step onto each other's toes... A good design document can be very short and much easier to understand than code, i.e. when you explain memory layout and do data oriented design.