Default values in ad customisers allow you to provide an alternative value for each piece of customised text in your ads. So even if you are not using a data feed, your ads will always show.
Let's say that you're running a campaign to advertise your sweet shop, and you have an ad group that promotes your chocolate sweet products. The snippet of code that you'll insert in your ad text might look like the following:
{=ProuctFeed.CandyType:Chocolate} Doing this means that Chocolate will show when the type of confection can't be inserted in your ad.
Default values are optional. However, if an ad contains more than one ad customiser, default values must be provided for each customiser.
