Goals keep us honest and focused on what's the task at hand. It gives us a purpose to focus our efforts and a metric that keeps score. It gives something for us to strive towards, when there is uncertainty.
Goals can change over time, in fact they should. If they don't change, growth is stunted. No goals mean very little to no growth.
Sometimes the goal itself isn't the point, but the process in striving towards that goal. The process allows us to consider how we would reach that goal, consider the constraints there may be, and find a way around those constraints first. Thus, when you are ready to achieve that goal, the process is already clear.
Setting a larger goal is better than a smaller goal. A larger goal stress-tests the processes to achieve the goal, whereas a smaller goal is oftentimes sufficient with a pre-existing process. A larger goal expands the mind to what's possible, whereas a smaller goal keeps us towards the status quo.
Setting a short term goal is better than a long term goal. A short term goal allows you to sprint and focus on achieving that goal, with a 100% mind, and allows you to change the longer term goal if the situation changes.