Re: Display Ads
Radius Targeting is one of the technique which can be used to effectively target your audiences when you know that the range of audiences can vary within a certain area which can covered using certain miles or kilometers as this targeting method provides.
Rest is when you start using it and start displaying ads, then you will have to identify the effective regions of your conversions. This can be done once the ads are displaying to the users and how are they performing in terms of effective clicks, conversions, bounce rate etc...
The fact is that once you don't try you won't be able to understand how they are performing. There are other effective ways of targeting as well, where you can see which target regions you can select directly and which not.
Location Target types can vary from country to country which you can find here and then decide which option you should choose to effectively target your Google Ads: https://support.google.com/adwords/answer/1722075