Short answer: you can connect their outputs, for example to form wired logic or create busses.

The more common logic outputs, like TTL totem-pole outputs or CMOS outputs are bidirectional. This means that it will try to connect the output to the HIGH or the LOW voltage levels (exact values depend on the family), in a low-resistance path. If you connect two of those outputs together, an unfortunate case can happen when one is trying to push HIGH and the other is LOW - thus creating a low-resistance path between the two, resulting in damage of the circuit - notably one of the output drives is very likely to fail.

Open-collector or open-drain outputs in contrast can only pull current. This means you need an external pull-up resistor to create the HIGH voltage level (and you can choose it's value and power rating, witch might come useful in some situations). This means it's safe to connect their outputs, and that actually forms an AND-gate, since if any of them want to push LOW, it will become LOW (assuming positive logic again). This means it's super easy to create a 8 input AND gate from OC outputs, witch might come useful in some situatuions.

Another possible use is the creation of busses. The simplest example I could come up with is an interrupt line for a processor. Many devices might want to trigger an interrupt (timers, peripherals, etc.), but there's only one interrupt line. If every device uses open-collector outputs, then any of them can pull the line down to trigger an interrupt. More complex examples might include multi-device busses like I2C where any of the devices might want to talk to the rest of them, but plain old PS/2 keyboards also use an open-collector interface for 2-line bidirectional communication.

I must mention that it's possible to do all that without OC/OD outputs, but might be harder. Wired logic can be replaced with gates, and OC busses might be implemented with tri-state logic instead (where we have HIGH-LOW-Z modes, the later being "pretend I'm not even here") - but then extra work might need to be done to ensure that at a time only one device want to drive the bus. With OC outputs, big logic gates can be avoided, and mistakes on bus driving only corrupt the data but not damage the devices.

Also, some OC devices might have higher voltage tolerances, for example the 74x41 BCD decoder can drive 70V for Nixie tubes.

Short answer: you can connect their outputs, for example to form wired logic or create busses.

The more common logic outputs, like TTL totem-pole outputs or CMOS outputs are bidirectional. (clarification: I ment they can push and pull current, not that they can be used as inputs) This means that it will try to connect the output to the HIGH or the LOW voltage levels (exact values depend on the family), in a low-resistance path. If you connect two of those outputs together, an unfortunate case can happen when one is trying to push HIGH and the other is LOW - thus creating a low-resistance path between the two, resulting in damage of the circuit - notably one of the output drives is very likely to fail.

Open-collector or open-drain outputs in contrast can only pull current. This means you need an external pull-up resistor to create the HIGH voltage level (and you can choose it's value and power rating, witch might come useful in some situations). This means it's safe to connect their outputs, and that actually forms an AND-gate, since if any of them want to push LOW, it will become LOW (assuming positive logic again). This means it's super easy to create a 8 input AND gate from OC outputs, witch might come useful in some situatuions.

Another possible use is the creation of busses. The simplest example I could come up with is an interrupt line for a processor. Many devices might want to trigger an interrupt (timers, peripherals, etc.), but there's only one interrupt line. If every device uses open-collector outputs, then any of them can pull the line down to trigger an interrupt. More complex examples might include multi-device busses like I2C where any of the devices might want to talk to the rest of them, but plain old PS/2 keyboards also use an open-collector interface for 2-line bidirectional communication.

I must mention that it's possible to do all that without OC/OD outputs, but might be harder. Wired logic can be replaced with gates, and OC busses might be implemented with tri-state logic instead (where we have HIGH-LOW-Z modes, the later being "pretend I'm not even here") - but then extra work might need to be done to ensure that at a time only one device want to drive the bus. With OC outputs, big logic gates can be avoided, and mistakes on bus driving only corrupt the data but not damage the devices.

Also, some OC devices might have higher voltage tolerances, for example the 74x41 BCD decoder can drive 70V for Nixie tubes.