It can be a good way for people to be targeted on what they are about to do if they are targeted in the appropriate way. A company called bluekai sells this kind of data but it is really alot of junk from what I have seen. There are ways though to know when someone has already completed an action or has the intent to complete an action. You might also know that someone will be in a specific city that is not their home, where ads can be targeted.

But I do agree that in the past and to this day there are many ads that lack the appropriate context to be retargeting you on ad networks.