Apply actuals

Hi Everyone，

I am confused with tools "Apply actuals". Ususlly, i didn't use "Apply actuals" to update shcdule, I just update each acitivity manually, and then click "scheudle". 

These days,one guy told me the right prodedure to update progress should be via "Apply actuals" tools. So, i followed his advice, but when i update progress, i change the actual date of each activity manually, and then click "Apply actuals" tools, the actulal  date i just changed manually will be automatically updated and repalced with baseline date.

 

Thanks