The most efficient workflow depends entirely on the shot. Rotobrush is a semi-automated tool that will work fairly well if there is sufficient contrast between the subject (the cat) and the background. Sometimes you have to combine techniques. You may be able to use channel effects or levels to create a matte. You may need to create masks and animate them by hand.
If you want to remove the background from a shot that was not shot with removing the background in mind it can and often does take a lot of time. I've worked on 3-second shots that took the better part of a day. I've used Rotobrush on 10-second shots that took less than a half-hour. Show us a screenshot of the footage*, or better yet, show us the footage and we can point you to a solution. Any technique you use is going to require a good understanding of the UI and standard workflow in After Effects.
* The "Drag & Drop here..." area is buggy and should not be used to share images. Please use the toolbar or just drag your images to the reply field.