Petrol is around £7.00/gallon. Assume the average car does 40 to the gallon (and neglecting any other costs of running a car, and the value of your time.) That is about 17.5 p/mile
For 60p you can deliver a letter personally (and
tbh quicker!) within about a 1.5 mile radius of your home. After that it is still cheaper to use RM 1st class. Seconf class it drops to about a mile (but much slower)
I occasionally buy stuff from Novatech, about a 30 mile round trip, either because I need something now, or just to save their delivery charge (about £6.00 for next day) but that is only slightly more than collecting it myself.
Put in that perspective, courier and postal charges are still low.
What the charges might do is reduce junk mail, although bulk mailing rates are much lower than normal postage chargesso it might make a difference.
I am still surprised that RM don't offer discounts to Smartstamp users, instead thecharge a subscription which seems nonsensical to me!