ROAS is the simplest answer to "did the ads make money?" — gross revenue attributable to a campaign divided by what the campaign cost in media. A ROAS of 4 means each dollar of spend returned four dollars of revenue, before margin.
For agencies, ROAS is the metric every paid-media conversation starts with — and the metric that hides the most. It does not account for product margin, it lumps existing customers and new ones together, and the "attributed" revenue depends on the attribution model behind it. The same campaign can show a 2× or a 6× ROAS depending on which window you choose.
The honest version of ROAS pairs it with margin and incrementality: revenue × gross margin minus ad cost, run on customers the campaign actually brought in. Most boards do not see that number, but the agencies that quote it tend to keep the account.