There is a huge difference between a true scheduled rest day, and a skipped session. Do not skip sessions ever. Consistency is crucial and one of the main reasons that so many people fail each year in the gym. A true rest day is designed to recover the body, develop new muscle tissue, and add strength. It is a very necessary part of any workout program in order to not hit plateaus and grow.
A skipped workout is a nasty habit to get into mentally. If a person skips once or