Question : Do I have to use the Play Speed points?
Answer : No. You are not required to spend these points but it is suggested for statistical accuracy. I personally use these points in every game I have played. Even when a team is behind and they have a slow down offense. This really comes into play with older teams. Example : 1945 Army has a +52 for their play speed. They will have 52 plays where they can speed up the clock (take more time off). That will pretty much take more time off the clock on every offensive play they run. If you do not, then this team will beat other teams by 70 instead of the 40 they did in real life.
Play Speed 
How does this game play solitaire? Is there a defensive play selection chart based on down and distance? Just curious as I’m considering a purchase…
Well over 90% of the players use the game solo. It plays very well. There are some “house rules” that various folks use to help with playcalling. The best resource for these is our facebook group where people share a lot of their insights. https://www.facebook.com/groups/SaturdayLegendsSaturday Legends Facebook Group