Skipped Workouts VS Rest Days
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 twice they fall into that pattern whenever they do not feel up for the gym. Think of it this way, if you miss one workout each week for an entire year you will set yourself back roughly 7 weeks of training that you missed out on. That time could have been used for added structure and progressive overload training to make reaching your goals much easier. Rest is great, but skipped sessions are terrible. Unless you are truly sick and need recovery due to illness, you must get your training in. The body needs to know that there is a demand being placed on it regardless of the mental state of mind and energy of the body that day.
A scheduled rest day is fine, but skipping multiple workouts each month will put you miles behind in the grand scheme of things that year. Militant, dedicated, and consistent. These are the major keys.