Different sections aren't required, but can be helpful, depending on what your goals are. For example, you might want a filter sock in a deeper section for particulate filtration or carbon. Baffles can be helpful in eliminating bubbles that might get sucked into your return pump. Baffles can also be a good place to place sponges or egg crate to keep critters from wandering too close to your pump.
Different water levels are also helpful in running different types of equipment because some things have different water depth requirements.
Also, a smaller chamber for your return pump shows water level changes (from evaporation) better than a single open sump would do. That makes it easier to maintain super consistent TDS if you are manually replacing top-off water.
Lots of other benefits, but not one are a must.