Here is what i keep reading a lot of articles about app-ads.txt
Authorized Sellers for Apps, also known as app-ads.txt, is an IAB initiative that helps protect your app ad inventory from ad fraud. You create app-ads.txt files to identify who is authorized to sell your inventory. Identifying authorized sellers can help you receive advertiser spend that might have otherwise gone toward counterfeit inventory of spoofed apps.
Use of app-ads.txt is not mandatory, but is highly recommended, especially if you are concerned that others may be spoofing your app.
So yes maybe affect your incomes if you do not include it.
If you mean what the txt file include
Sign in to your AdMob account
Click Apps in the sidebar.
Click View all apps.
Click the app-ads.txt tab.
Click How to set up app-ads.txt.
Click Copy next to the code snippet to copy.
Paste the code snippet into your app-ads.txt file.