Train (TGV) travel in France

As the man in seat 61 says, "I consider it 'sharp practice' that TGV limits the number of pass holders allowed on the train." There is a set limit (could be 0 on popular runs) that are allocated for each train. Once that number is reached, you wait for the next train even if it departs with lots of open seats.
http://www.seat61.com/Railpass-and-Eurail-pass-guide.htm#Should you buy a railpass or pay-as-you-go

SNCF (French National Rail) no longer honors the 3-5 country pass. It does honor the France pass and 2-country passes that include France. If you have a pass that includes France and you wish to take a TGV, you will have to buy a seat reservation, either at a station in France or in advance from a broker like Rail Europe. However, as Sam said, SNCF limits the number of seats it allocates to pass holders. For detailed information, click on the Rail Passes tab at the top of the page you're reading now. And read the information on seat61.com. If you book point-to-point tickets well in advance (up to 3 months allowed) on tgv-europe.com, you can get discount fare tickets that will cost you much less than any pass. What is your itinerary? Will you be traveling outside of France?

We are traveling in France only in mid-to-late July. I already had purchased a 3 day pass to travel around France. We were hoping to be able to take the TGV from CDG on the morning of arrival to Avignon. The faster we can get to our lodging, the better. :-) I will check out The Man in Seat 61. Thank you!