Taking the coffee tables - if you want to buy in bulk, you will get the benefit of bulk pricing, but you then have to pay for storage and any/all handling between storage and end point as opposed to buying from Tesco homeware when they have to bear those costs and stick them in the price, and, of course, delivery charges.
To make an in-house system work smoothly, you always need surplus capacity in the system, which, in turn, has to be paid for unless the concept of long delays is acceptable. The downside there is human nature, under Parkinsons Law, which ensures that the needed surplus capacity will always be taken up doing something pointless. My addition to this law is that this pointless filler will become the main objective, and to fulfil the real objective, the department size will "need" to be increased, and along with that, its budget. The process is beloved of senior management, and is known as empire building.
Then there is the cast iron audit trail, very necessary given the human acquisitive syndrome, but it has to be remembered that cast iron is known to be brittle.....