Those flights can be useful if travelling from regional France to CDG to self-connect to a flight which doesn't interline with a suitable schedule (or doesn't interline at sensible prices) with Air France.
As an example, trying to combine Air France and Easyjet on the same ticket is not worth trying. However, 2 separate (modestly priced) tickets, and it's sometimes worthwhile. Connecting from somewhere like Montparnasse across Paris to CDG by metro / RER is a pain