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One advantage which Coase explicitly mentions in his classic paper on why a firm might provide a lower cost solution to direct bilateral markets contracts has to do with long term contracts.  It may be cheaper to replace a series of spot or futures contracts with an in-house longer term one which fixes in the costs of the factor of production.

Is this a real advantage?  Assume for the moment that the futures price of the factor of production in the market place is the fair value of the factor.  

The argument goes like this.  We need some factor F to make one of the corporate products.  There is a spot price $S_t$ for this product right now.  We need it for a series of t periods in the future.  We might look to buy it on the futures market for expiry t.  There we assume (naively) a fair value of $S_te^{rt}$, using the risk free rate.  But, the futures market isn't infinitely deep - it peters out after a number of months or quarters or years.  Wouldn't it be better, more possible, cheaper, for a firm to internally charge for this?

My first thought is if those longer term contracts are needed by companies, then one of two things would happen. First, there might be a deeper (temporally) futures market.  Second, there is an OTC market which can (and does) service those needs which might exist, as it does currently for financial derivatives.  

My second thought: even ignoring that point, how does the company achieve a better price, all costs considered, than the market?  What is the company doing, other than taking a chance.  The hurdle it has to overcome is the cost of that futures contract, assuming it exists, for the corresponding time period, including all costs.  Companies in general can't take a chance and persistently win, on average.  The efficient markets hypothesis would see to that.  So on average, the average company will be no better and no worse off than the futures market would imply.  Otherwise the company is merely subsidising that particular factor of production within the the corporate balance sheet.  If this is persistent, how can that company survive long term? Luck is not on the side of the average company, so if it is internally charging $S_te^{rt}$ minus some benefit based on reduced contract costs, isn't this just putting the extra cost on the firm generally, socialising the cost within the firm?  Doesn't this just put the firm at a disadvantage, at the margin, to the degree that this is an economically significant benefit?  All this assumes that the average company can't produce the factor any cheaper than the spot price $S_t$ implies.

It leaves untouched the general argument for the deal costs - contract creation costs, the costs in general of getting the deal to 'the market'. 

Also with large corporates there's a real internal communication problem.  It is a version of the search cost all over again.  Large companies are a bit like 'the world out there' insofar as finding the right internal market has its own costs. And the larger the firm, the larger these costs.  This would be a drag in general on the size of the firm.