The idea behind the spindle locking pin is that it is an extra safety mechanism. If you lose one or both nuts and washers on the spindle pin it can't slide out, assuming you have one that can actually be removed without the use of a large press. I have used a bolt in mine an no pin or similar mechanism and have no plan to ever again. That said I do regular bolt/nut checks on my car as part of their maintenance, which a large portion of the public think is either silly or a complete waste of time. Probably the same people who shouldn't be driving an old car without all the modern nannies or insert version of onstar they need when they lock themselves out of their car because it doesn't need a key to start.