When each job is put into production it has to be finished properly so it looks right.
Whether the job is a flyer, a canvas or a catalogue each one is finished in another way.
Flyers are typically just a single sheet, so the only finishing would be the trimming.
Brochures are a single sheet however the finishing includes trimming and folding to the size you would like the finished project.
When a catalogue is being finished, how it is completed, is dependant on the type of binding you would be using. How it is bound is usually based on the thickness of the catalogue. If it is over a 60 pages depending on the thickness of the paper than you can not saddle stitch the job, it must be perfect bound or coil bound.
Other types of finishing options depend on the product. It could be the type of coating that you put on a project for either gloss or matte look. It could be a lamination, or a special cut for a special shape. So when you are printing something there are a lot of options that you can pick from to help you stand out from the crowd.