It is possible for there to be multiple benefits. In fact this is the most desirable, since when there is an immediate economic benefit to both sides, it is incentivized to happen.
In the case of supermarket self-scanning, sure, the supermarket can reduce costs.
However, the benefit to the customer is in a shorter total time through checkout. Entropy causes customers to arrive at checkouts in spurts, rather than there being a steady flow. It is expensive for stores for checkout operators to remain idle (and would be passed on in higher prices). So customers have to queue instead of there being more checkout operators available during spurts.
On the other hand, the cost of maintaining extra self-checkout machines costs very little. So in practice, they tend to be available to handle spurts of activity, resulting in faster overall checkout times for customers too.
For the stores: yes, reduced costs. For the customers: reduced costs result in lower prices in healthy markets, and also time to traverse checkouts is faster.
The same can be applied to airlines. Fewer staff at the line at the gate results in reduced staffing costs: sure. But also: less standing around in lines and less juggling at the front of the line (especially for the infirm, or those with kids, etc) is also a clear benefit to passengers.
It is cynical to ignore the other half of the benefits and focus just on costs. And in any case, reduced costs for the company results in lower prices for consumers.