Almost every insurance policy requires the policyholder to bear the first portion of any claim. That threshold does several distinct jobs, and reducing it is rarely free.
Small claims cost more than they pay out
Handling a claim involves notification, assessment, possibly an inspection, and settlement, and that administrative cost is largely independent of the claim's size.
For small amounts the handling cost can approach or exceed the payment itself, which makes the transaction uneconomic for both parties.
An excess removes those claims from the system entirely, and the saving is reflected in the premium charged to everyone.
It keeps the insured exposed to the outcome
Full cover from the first unit of loss weakens the incentive to prevent losses, since the consequence of carelessness falls entirely on the insurer.
Retaining part of every loss keeps the policyholder's interest aligned with avoiding it, which reduces the frequency of claims across the insured population.
The effect is well established in pricing, which is why policies with higher excesses cost less by more than the arithmetic of the retained amount alone would suggest.
It filters exaggerated and marginal claims
A threshold discourages claims where the loss is uncertain or the amount is inflated, because a small exaggeration produces no benefit if it stays below the excess.
It also removes claims that would otherwise be made simply because cover exists, where the policyholder would have absorbed the cost without complaint had there been no policy.
Reducing claim frequency matters more than reducing average claim size for most consumer lines, since frequency drives the administrative burden.
Compulsory and voluntary portions differ
Many policies combine an amount the insurer requires with an additional amount the policyholder chooses in exchange for a lower premium.
Both apply to a claim, so the total borne is the sum rather than the larger of the two, which is a frequent source of surprise at the point of claim.
Choosing a high voluntary amount only makes sense where the policyholder could actually meet it without difficulty, since the saving is realised annually and the cost arrives all at once.
Claiming has costs beyond the excess
A claim usually affects future premiums and can remove accumulated discounts, so the effective cost of claiming exceeds the retained amount.
For losses only modestly above the threshold, paying directly and preserving the claims record is often cheaper across the following renewals.
Insurers generally still expect notification of incidents even where no claim is made, and failing to disclose can affect cover later, which is a separate obligation from the decision to claim.