We used to send several thousand parcels a day through RM, each was insured for £28 at the time, we used to send any small item(s) up to £40 in value that way. The cost saving on the courier was over £2 each so they could effectively loose quite a lot of them before it had any commercial impact.
The other good one was with Shitty Link they had a guarantee that every parcel would be delivered next day, they even sent a file back to us at the end of the day with all the results, so we parsed the file & claimed back for every one that wasn't delivered, involved no humans & no cost.