Hi @kazurayam
The setting in Project > Setting > Execution for Smart Wait will take effect for all test cases. While if you disable the global setting, and use the smart wait enable/disable keywords in your test case, then only the section of code between these two keywords will be affected by the smart wait functionality.
Internally, the Smart Wait functionality waits for the page to become static within some timeframe, so that the phenomenon where elements are not present, or some loading overlay prevents clicks/actions to reach the desired element would present less.