When we have two campaigns that are dependent on each other, our company uses one of these triggers to request the subsequent campaign: the Request Campaign action, or Add to List in Program x. When we Add to List, the next Campaign looks for that cue, and it is then triggered.
I always wondered what the benefit was to use "Add to List" as opposed to "Request Campaign." The intuitive benefit is that in using Static Lists, you are able to make faster reports, and have a trustworthy log of all your members. At the same time, Request Campaign always seemed cleaner.
I recently learned that having too many "Request Campaigns" within your running campaigns can severely slow down your instance and cause a massive Campaign Queue!
So, if you have a larger Marketo instance, make sure to consider creating Batch Campaigns that add to list, instead of requesting a campaign!