Back in the days of TTL, most devices would source approximately 1.2 mA of current, yet would sink 16. LSTTL was somewhat less capable, but not much. However, if you wanted to drive an input with open-collector outputs, those only sink current, and source none. This, otherwise known as "wire-OR'd" connection, allowed you to drive a single input, e.g. a /RESET or /IRQ input which often had to be shared, from multiple open-collector, or open-drain outputs.

The combination of the speed advantage due to higher output current, and the ability to "wire-OR" (in negative logic) the connection was a big influence toward the generalized use of "active-low" control signals in the TTL days. The wire-or capability persists, though todays CMOS devices generally can source as much current as they can sink.

RE