[torero]

Interesting question. I know a trader who uses indexes to mark his resistance and support and watches them. He continues to trade the futures based on its own price action until the index arrives at these levels, he pays more attention to them and possible for an exit. The influence may be there if prices are rejected and reverse, it could influence the futures to halt and consolidate or reverse as well.

As for after hours, depending on the market. If the market has lots of activity outside the regular hours due to foreign involvement (grains, forex, etc). If so, these price highs and lows may be affect prices into the regular hours.