Idle hands...

Be extremely careful not to waste even a moment. You should view even ten minutes of wasted time as a grave sin (Heaven preserve us). You pay for wasted time with your life. The time that you have thrown away, a part of your life, is gone forever; you will never regain it. Remind yourself of your mortality. This day and time are fading away, and you cannot bring them back. 

If you have wasted time, imagine that you have cut out a strip of your heart and thrown it to the dogs. - Reb Kalonymos Kalman Shapira, B'nei Machshava Tova

This excerpt sent chills up my spine as I read it between aliyot this past Shabbos. Thankfully my busy schedule doesn't necessarily afford me any considerable free time, but in those few moments where there is a lull in activity, I know that I don't always capitalize on that time properly. When the rebbe puts it in such a perspective, this whole matter becomes an issue of v'nishmartam!
As the rebbe stresses numerous times in this sefer as well as in his other writings, boredom and sitting idle is anathema to Judaism...