Owning things that you use infrequently is inefficient. If you could rent or borrow it for the actual time that you need it, then you are wasting (time|money|other) if you own.
Unless you can rent it out when you aren't using it, in which case owning it may be more efficient.
Both sides of the same coin. Own and rent it out, or rent-when-you-need. The net of these two in action reduces overall waste.
Roughly, if two people need to use a car half-time, it is more wasteful for them to own separate cars than to arrange to share one.
Only if the "half-time" is consistently and predictably non-overlapping without interfering with the efficiency of whatever operation produces the need.
But if there is some uncertainty and/or overlap it's still not necessarily a deal breaker- you can buy a lot of bus passes for the price of half a car.
Sort of like by using a schedule? Posted online? On one convenient website? Like airbnb?