Is it necessary to use "start_activity"?

Hi,

I am using Python 3.7 with appium. After I defined my desired capabilities, I noticed the application is open when I call:
driver = webdriver.Remote('http://localhost:4723/wd/hub', desired_caps)

and then y automation test start without issues.

So I was wondering why to use:
driver.start_activity(“com.app.android”, “com.app.mainactivity.MainActivity”)
?

Because when I write the 2 lines:
driver = webdriver.Remote(‘http://localhost:4723/wd/hub’, desired_caps)
driver.start_activity(“com.instagram.android”, “com.instagram.mainactivity.MainActivity”)

I can see Appium launching 2 times the app. So I make the conclusion that it is useless to write a line of code with “start_activity”.

Can someone explain me the difference and in which scenario I should use “start_activity” as the declaration of driver with the line:
driver = webdriver.Remote('http://localhost:4723/wd/hub', desired_caps)
is enough to start the application and run the test.

Thanks for helping me to understand better appium.