My understanding is that it just saves Supplies having to go out to tender or get 3 quotes if somebody is already on it Ian.
We aren't on any because of the requirement for long term fixed pricing with no get out clause if the exchange rate crashes.
This is causing us a few problems because at least 1 of our competitors is and they are much cheaper to buy,we don't normally lose customers for long though once the euphoria of the cheap price has worn off.
Also as you seem to understand some take a % cut which artificially raises the purchase price quoted.
Interestingly just in case you haven't heard Bunzl are contesting the Supply Chain "One Stop Shop" monopoly plan as being anti-competitive because they are top slicing Trusts so effectively if you use Bunzl or say TPS you end up paying twice for delivery and on costs.
www.healthtec.co.uk