Whether your program should be a listing or a session is a consideration based on multiple factors including marketing need, program types, or customer experience etc.
Generally speaking, a listing is for a different type of program. And a session is for a distinctive period of time (so as pricing). For example, if you run a dance studio, you may have different listings for different types of dance (ballet, jazz, etc.), but can have sessions for winter vs. spring.
You always want to give choices for your customer that are clear and no more than necessary.