Query related to Battery of 16 inch MacBook Pro

i am using a 16 inch Macbook pro from a month and what i'm worried now is when i'm connected to an external monitor the battery life goes down to 3-4 or even less if i'm using something which requires high performance i found this as normal because of it's switching to high performance graphic card and now since my battery life is going down rapidly,

Is it a good practice to use the laptop when it is plugged in and how does it function?

if i'm plugged in will it bypass the battery and use the power adapter to run or will it still be using the battery to run ? And how will it(Plugging in and using my Mac) affect my battery life?

Hope you will answer me.

Thanks in advance.