Important uses for SASEs are when requesting information about products or services, or when sending manuscripts to literary agents.
SASEs are used when communicating with companies, charities or celebrities (for fan post), in cases where each recipient can afford the cost of a single stamp and envelope, but it would be a burden on the organization to pay for the postage on all the letters it sends out.
In the case of amateur radio, operators will send a SASE when requesting another station's QSL card.
SASEs cannot easily be used for international mail, since senders rarely have supplies of mint foreign stamps.
Instead, international reply coupons (IRCs) can be purchased at post offices, although they are no longer sold in some countries, including the United States.