It would be useful if limits on iframe were sent along with iframe request. For example website owner restricts all iframes to 100kb to make sure that ads are small (I assume iframe === ad here). But ad servers have no idea about limits and will return bigger ads. At the same time if ad server new about restriction they could have either server smaller ads (if possible) or just return empty response saving bandwidth and cpu.
It would be useful if limits on iframe were sent along with iframe request. For example website owner restricts all iframes to 100kb to make sure that ads are small (I assume iframe === ad here). But ad servers have no idea about limits and will return bigger ads. At the same time if ad server new about restriction they could have either server smaller ads (if possible) or just return empty response saving bandwidth and cpu.