There are a variety of benefits that arise from this:
- First and foremost, you get the benefit of crowd-sourcing. If you go to add an aircraft and it's already in the system, you pick up that aircraft. My working assumption - strongly validated in practice - is that the existing definition is more accurate the vast majority of the time. So, for example, if you enter a C-172, but it's already in the system as the more-specific C-172P, you'll get the C-172P.
- Crowd-sourcing has another benefit: if another pilot spots an error and fixes it, you get the benefit of the fix. A variant of the prior example is that you have a C-172 in your profile and somebody else updates it to be the more accurate C-172P, you get the benefit of the change. Again, in practice, probably 90+% of such changes are in the direction of greater accuracy.
- As pictures of aircraft get added to the system, everybody gets the benefit.
- Shared aircraft enables people who actually share an aircraft to keep track of maintenance and inspections, such as VOR checks.
- Club functionality would be impossible without shared aircraft.
There's a tradeoff here, of course. The obvious downside is the fact that changes by one pilot can impact another's logbook. So if N12345 was a Cessna C-172 and the registration gets re-assigned to a Boeing 737, and pilot #2 changes N12345 to be a 737, then suddenly pilot #1 has some extra multi-engine/turbine time in their logbook!
However, in practice this is a relatively small problem and easily managed. I receive a notification of - and review - EVERY change made to an aircraft that has more than one pilot flying it. (It's actually not all that much; a few edits a day, most of which are of the C-172 to C-172P variety described above; i.e., requiring no action).
So I can wade in when necessary to keep everybody straight. And when the same registration is used for multiple aircraft (such as the 172 to 737 example), I can "clone" the aircraft across both models, so that each pilot can have the correct model for their logbook. Pilots can even have both models side by side, if it's appropriate, such as when they take a vanity registration from one aircraft to another, or if they have a plane that is on floats half the year and wheels the other half.