It is believed by many that insurers make profit from the difference between the money they receive in premiums, and the money they pay in claims.
This is true, but it is not the primary source of income for insurers, which perhaps causes the misguided notion that insurers make millions (and billions) of dollars in profit, at the expense of those people whose claims are denied.
Insurers are very liquid (or cash rich) businesses, owing to the regular volumes of cash they receive for policies they underwrite. Insurers then have to set aside some of this money to pay claims, the minimum amounts of which are set by law. This is called 'regulatory capital'. The rest they invest and that is the primary source of an insurer's income.
If reserves are set too high then too much regulatory capital is held up and this reduces the insurer's investment capital and their ability to make money. If reserves are set too low, then insurers may not be able to meet their regulatory capital requirements or satisfy claims.
Therefore, the importance of accurate reserving cannot be underestimated and having an #actuary on board makes the whole difference.