Why would you possibly need to use this feature?
If you have your own data analytics platform, where you are measuring costs, in-app events and all other important stuff, you would possibly need to attribute specific installs to a specific cost category.
For example, you have a travel app with different products - flight tickets, train tickets, hotels, car rental service, hostels and so on. Each product should have its own calculated cost to measure ROI of acquired installs, and to calculate costs of each separate products in your analytics platform you are using specific source tags - _flights, _trains, _hotels and so on.
In this case, you would need to use suffix/prefix tool to add those tags to ad group level naming
Activate suffix/prefix toggle and type the tag
If you will create SKAG structure with those settings, your ad group naming will have «flights_» in the naming, which will help you to attribute the costs for the needed product
This setting will affect only on the ad group naming, your keywords will be ok
