Before AdWords introduced the Enhanced Campaign (EC), the typical practice was to have separate mobile and desktop campaigns. Ads in a desktop campaign would have destination URLs for landing pages optimized for desktops.  Ads in a mobile campaign would have destination URLs for landing pages optimized for mobile devices.

With AdWords new Enhanced Campaigns, it's impossible to target ads to mobile devices only. As long as your campaign mobile device bid adjustment is anything other than -100%, an ad could potentially be served to any device type. Advertisers are asking themselves, "Why can't I specify two URLs for my ads, one for desktop, one for mobile?"  This is actually possible. The answer is to use the {ifmobile} ValueTrack parameter. Here's how it works...

LEGACY SCENARIO (multiple device-specific campaigns)

URL for an ad in a campaign that targets DESKTOPS:

http://www.testsite.com/en/US/abcdef/index.html

URL for an ad in a campaign that targets MOBILE DEVICES:

http://m.testsite.com/www.acme.com/en/US/abcdef/index.html

EC SCENARIO (one EC campaign for all devices)

URL for any ad:

http://{ifmobile:m.testsite.com/}www.acme.com/en/US/abcdef/index.html

When this ad is served to a mobile device, the string "m.testsite.com/" is inserted in the desktop URL, turning it into the mobile URL. The key thing to keep in mind is that the mobile URL must contain every character in the corresponding desktop URL plus an additional segment, i.e. the argument for {ifmobile}. If desktop and mobile landing pages are structured so that the difference between the URLs is always the same string, the same argument can alway be used in {ifmobile}.