How do firms make payments to one another? Do they actually pay cash? Do they transfer deposits from one account to another at a bank?
An important characteristic of the economy is the time lapse between the production and consumption of goods. Production always precedes consumption, hence producers produce in anticipation of some levels of consumption. Similarly, retailers who stock these consumer goods expect to sell those products in the market in the future. So, at every level of the chain from production to final consumption, there is a element of time-lapse in their cash commitments and cash inflows. How is this managed?
Suppose firm A is a retailer and firm B is a wholesaler, trading in goods and both have an account at a ‘Bank’. When firm A buys goods from B, it does not have the requisite money in the form of cash to pay B. So, it might issue ‘Bills of Exchange’ which is a promise to pay B the cost of goods bought, say in 90 days. The balance sheets of A and B may look something like this:

If the Firm B is satisfied with this, then there is no need for a bank. However, B might need ‘liquid’ cash in the form of currency notes to pay somebody else which Bills do not provide as they are ‘illiquid’ for its term (here, 90 days). Or B might not be sure if A will repay the amount. So, B might look for a entity to discount the Bills and provide it with cash.
Enter the Bank:

What incentive does bank have to do this transaction? Notes are zero-interest assets for the bank. When the bank discounts bills, it acquires an interest paying asset. However, the Bills are not means of payment for the deposits it has as liabilities – only notes can serve that purpose. So, the transaction of Bills for notes has an element of liquidity risk for the bank i.e. it may not have sufficient notes to satisfy the withdrawal demands of depositors.
How might the Bank reduce this risk? Instead of paying notes to B, what if the Bank opens a deposit account for B? What does B’s and Bank’s balance sheets look like then?

In this iteration, the Bank promises to pay notes, instead of paying notes immediately. This is a way for the bank of economize its note issue. This adjusts the liquidity risk of the bank, but only slightly. Is there another way?
What if the Bank guarantees the Bills of Exchange by ‘accepting’ the Bill, saying something like – “If the firm A does not pay the Bill on maturity, I’ll pay”. How do the balance sheets look like then?

In this case, if A isn’t able to pay the amount mentioned in the Bill, the Bank has to pay it on the maturity of the Bill. So, the bank does not have to worry about liquidity for the term of the Bill (here, 90 days). This is similar to time deposits, which can be liquidated only after a certain time period, although it is contingent on A’s business in this case. This is very similar to the more complicated Credit Default Swaps (CDSs).
But why would Bank engage in this transaction? B pays Bank a ‘premium’ (fee) upfront for guaranteeing a future payment. So, if Bank can judge well that A will pay on time, this business seems without much risk. Worry for the bank is if A is unable to pay on time.
We see that in these iterations that Banks provide firms with liquid assets (notes/deposits) in exchange for illiquid assets (Bill of Exchange) allowing for balance sheets to expand temporarily for trade to happen and then the balance sheets contract when A makes the payment.
On completion of first iteration, the balance sheets look like this:

In case of deposits, the balance sheet look like this:

In case of ‘acceptance’, if A repays the notes to B, the guarantee of the Bank is not invoked and the balance sheets look like this:

In this case, A’s ability to pay in notes becomes vital for B because it determines whether B will have to invoke the ‘guarantee’ with Bank or not. So, unlike previous iterations, B is dependent on A for future cash inflows. If A does not pay, then the balance sheets look like this:

In this case, B has an alternate source of liquid funds from the Bank – which can either supply it with notes or open a deposit account (much like it did in the second iteration!). Also, note that while the acceptance is invoked, the Bills of Exchange remain unsettled and shift to the balance sheet of Bank which is better able to bear it. We can also see that the problem here is not necessarily of A defaulting, but of A having to delay its payments and disturbing the timeline of cash inflow of B.
So, in these temporary expansion of balance sheets on both sides,the Bank provides both firms A and B with elasticity to carry out their respective trades in the market while enforcing discipline on them when Bills mature. We should not forget that these are not the only balance sheets in the market.
Different Bills mature at different points in time, so the Bank knows when it can expect to receive cash. On the liabilities side, it can broadly predict the withdrawal preferences of its depositors. To match these cash commitments with cash inflows, not just in amounts but also line them up in time, is the very essence of banking.
Reference:
- Mehrling, P.; Course: ‘Money and Banking’ at Barnard College – See
http://www.perrymehrling.com/