Q:

Is there an overhead when calling boto3.client()?

Just a simple and short question:
Should I call boto3.client() once and reuse the client or is it okay to call it every time I need to access the client?

A:

You get charged for API calls you make to AWS. Simply calling client object is not charged. So you can make multiple calls if you want to. However, it make more sense to create one client variable and use it multiple times. 

