Are neutral service bikes actually useful? In the races I've watched, occasionally a rider who has suffered a mechanical will be given a neutral service bike to continue racing on. I always wonder if this does any good because the rider never seems to make it back onto the peleton or breakaway group.
This article from bicycling.com says:

Generally, the rider will stay on the neutral service bike for only a few miles before pulling over in a better spot and exchanging it for a team-supplied spare with the correct fit coordinates.

I've never noticed this happening, but that may be because I mostly watch women's racing, and maybe they don't have as many team spare bikes at the ready as the men? Nor have I ever noticed anyone crossing the finish line on a neutral service bike (although I'm sure that does happen).
My question can be answered with the following: has a rider on a neutral service bike ever gotten a top-10 result or been able to sufficiently perform domestique duties, directly assisting a team member in getting a top-10 result?
In my research, I found two interesting incidents in which the service bikes were unhelpful:

Fabio Aru &quot;couldn't really pedal&quot; because of a high seat
Chris Froome's neutral service bike had Look pedals instead of Shimano

Note: since I'm new to cyling, I've probably made some incorrect assumptions here. Please feel free to correct any of them
The problem is the lost time due the break down. The question is 'can a ride catch up after a break down', the neutral support bikes gives him a chance, no matter how small.
After a breakdown, the rider has two choices - wait for a team support vehicle with a bike fitted for him, or take a neutral support bike and get moving (likely at a slower pace) while the support teams sort out a bike and arrange a suitable place to swap.  (I suppose he has a third choice - withdraw from the race)
From  a pure racing perspective, the answer is as simple as filling in the variables - Lost time waiting vs lost time on the slower bike and a second bike swap. In some cases the second swap may cost more than the slower bike, in which case finishing on the neutral support bike would be pragmatic.  All this is easy to say on paper - in the heat of the moment this is all a judgement call.
However, the neutral support bike has a significant safety advantage where the breakdown has occurred in a location that the support team cannot get well clear of the other riders. The rider and neutral support team can be cleared from the dangerous situation in the shortest time possible, and a safe location for the riders support team to setup the bike and hand it to him can be chosen. The pressure to get the rider moving comes off the riders support team, who may compromise safety in the heat of having a rider standing around waiting for them. The team also have more time to set the bike up exactly right for the rider, so less chance of an incorrect configuration.