Right - the old rule of thumb used to be an Ethernet collision domain should have a maximum of five segments, with four repeaters, and three populated mixing segments (i.e. buses like 10BASE5 or 10BASE2), the other two segments being link segments (i.e. point-to-point like 10BASE-T or 10BASE-FL).

I think the idea was that anything more than this was likely to lead to long enough round-trip times between devices at the far ends of the Ethernet that the CSMA/CD algorithm couldn't be guaranteed to work.