Many people hate maintenance and wish to find ways to simplify it so they can sit back and watch their fish. Mainly this is an effort to save time and make the tasks of maintenance or controlling stability easier so that you can enjoy the hobby more. Many types of maintenance or changes in the water are stressful to the fish as well so anything to stabilize the changes and limit your time with your hands down in the tank stirring things up the better for your fishes "mental sanity".
Another reason someone might be interested in automation is so that if they go on vacation for several days or several weeks they can either A) monitor the fish and let someone know what to do to take care of it at home or B) monitor it and initiate automated controls to adjust the tank that either require manual initiation OR can do so on its own based on programming.
What else can you do? Fish Cam to let the world see your fish. Online tank data to show the world what your fish tanks are like for pH, temperature. Maybe even emergency measures in the event of failures of critical devices by activating spares, and more. The possibilties are as endless as your finances and your imagination (and technology) allow.
What you gain by selecting a task for automation varies depending on the work you had to do to do the task, how often you do the task, and how much effort you end up putting into the automation and testing to ensure the automation is working and what is it going to cost you to do that automation.
In your aquarium world many tasks are repeated over and over. Any of these tasks is a candidate for potential automation.
Some things that are commonly performed are things like feeding various live, frozen, pellet or flake foods, water changes, pH monitoring and adjustment, kH monitoring or adjustment, fertilizer dosing, temperature adjustments and more. Some types of automation are simply just methods of efficiency and distribution to improve a manual and sometimes complicated process. In these cases the automation is not really to replace the human work but to make it more efficient or accessible.
Sit back and make a list of everything you do. Think about how it would be better if you could have a way to do it without you touching it. Just because you have one type of automated way of doing something don't just accept that as the final answer. There may be better, faster, more efficient ways of doing it.