What are your related thoughts on all the bearings in the vehicle and brakes? Even with your note, I wonder why virtually all manufacturers require break-in.
The following video seems to make sense:
There's a Right and Wrong Way to Break In a New Car
To your questions...
Yes, I wonder why all the time as well the instructions are still there. My buddy and I are retired mechanical engineers from the Nuclear Power industry. We've been gear-heads since we were teens, drag raced, then road raced, built motors (I've got a 289 just out of my '67 Cougar that I'm putting in a 5.0 roller motor with a nicer cam as I type this). We both studied internal combustion engines in college and the like. He is an industry expert on lubricants and fuels since he took care (Corporately) of our emergency diesel generators. Our guess is that tradition dies hard - just like the 3000 mile oil change interval.
Bearing design in IC engines is such that the bearing metal NEVER touches the rotating element. The film of oil pumped in there provides the clearance desired (oil pressure, temperature and viscosity dictate). As such, there is no break-in for bearings. Touching of the metal parts is the initiator for serious problems and by design the proper machining during manufacture and hydrodynamic design preclude this. Oil starvation is your only concern here (without the proper high pressure film the metal parts will touch) - with today's engine designs oil consumption is more or less a long term concern.
Brakes should be normally driven for a while (avoid full on stops or significant downhill extended grades for a while first). Brakes have two components for 'break-in', both of which with today's technology have a relatively short time frame of import - bedding and cure. The bedding is where the mating surfaces become more or less the same (i.e. full surface contact). New brake pads will traditionally contact only a small amount of the rotor surface when applying (the alignment is not precise between these parts). There is some flexure as the contact load increases which will provide greater contact area. This is not critical because as you drive the surfaces quickly become mated such that the pads will fully contact the rotors. Initially, the smaller contact surface will have higher heat (due to the smaller localized areas), but the pad materials are designed for this and as such won't be an issue. Even if not fully mated, limited contact will simply enable the pad material to heat up faster to the target temperature and your friction coefficient has a broad temperature range so they work fine. Curing is where the friction material (pad material) off-gasses those non functional elements during early life (oils, glue, volatile byproducts, etc). This off-gasing (in extreme scenarios) can impact the pad performance. The pad material 'whitch's brew' of stuff (hard metals, bonding agents, etc.) releases the volatile agents at temperature; heat is the catalyst here. With normal driving, you won't even notice. The hotter you get your pads in normal driving, the faster they cure. Higher heat and number of cycles speeds if up.
If you're going to do some spirited driving or perhaps taking your new car up to mountainous terrain like we will be doing shortly into the life of the car, you can do some checks and accelerate the curing process. The check is do to a moderate to hard stop 1 to 3 times with the windows down. If you smell that good 'ol brake smell you may have smelled once before in the day OR you feel the brake effectiveness (torque) reduce a bit (brake fade), back off and resume normal driving. They're not fully cured yet (but they will still work fine other than the extreme breaking). If you want, drive around a couple more miles to cool them then repeat the process.
To cure new pads for racing (street compounds and more aggressive as well) I'd do 50% or greater level of effort stops from say, 30 to 50 mph all the way to a standstill and repeat. When I noted the slightest smell, I'd resume normal driving at 40 mph or so to cool down, then repeat again. Once we'd done the smell, cool, re-smell perhaps a dozen times or so we'd call it a day.
The only caution I'd have for brand new brakes is don't come down a 4000 ft. mountain with a lot of braking when brand new.
All street factory pads will bed themselves in and cure themselves within a few hundred miles on their own. What early bedding and cure does is allow multiple consecutive extreme stops without fade (which I doubt any of us will ever need). Yes, if you need to brake like the devil at any time due to an emergency - do it - they'll likely stop you fine even if you are driving your car home from the dealership right after purchase.
Sorry for the lengthy discussion.
