The software calculates area studies in two phases. The “sub-study” portion is the second phase of the study calculation. The tool builds the underlying map view based on the first phase calculations. Unfortunately you cannot turn this off but you can change it to run more quickly and give you more coarse results.
To do this navigate to Studies menu>Define Study Grid. When the dialogue opens, adjust your grid point spacing. The sub studies are related to your study grid resolution. The more fine your grid point spacing is, the more sub-studies will run, and the longer it will take. As a result, your map will look better visually. The more coarse your grid point spacing, the fewer sub-studies you will see run, and the process will go much quicker. As a result, your map will look more coarse.
In general, when you are starting a new design, it is best practice to start with a coarse study grid resolution so your study run times are fast. And as you reach the final stages of your design, increase the resolution of your study grid to generate a higher quality heat map for presenting.