Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Pioneer Energy Services (NYSE:PES) dropped as much as 10% during the trading day Tuesday following a downgrade from analyst group Jefferies.

So What: The Jefferies downgrade is just confirmation of something everyone has already figured out: declining oil prices would lead to declining rig activity. Since Pioneer's entire business centers on renting out drill rigs and other drilling-related equipment, reduced rig activity was bound to cause the company some pain. According to a Baker Hughes survey, just under a quarter of the rigs operating in the U.S. have been idled in the past three months alone. 

Now What: It's hard to say exactly how many of the idled rigs belong to Pioneer, but it's safe to assume the company will not reach its target utilization rate of 89% since close to a third of its drilling rigs were without a contract in the previous quarter. The company will report earnings next week, which will provide a better idea of how much this decline in rig activity is hurting Pioneer. Until then, it's certainly not worth making serious investment decisions on this stock.