Tubes do wear out when left on. The output tubes on an amp may last something on the order of 1,500 to 2,000 hours or so. The smaller tubes used in preamps will last much longer. 5,000 to 10,000 hours and more is probably not unreasonable. (There are just shy of 9,000 hours in a year.) Some specialty tubes can last tens of thousands of hours, but your equipment probably doesn't have tubes of that nature.
So, the question is how often you want to replace tubes and also how much electricity you wish to use. Your personal listening style is also a factor. If you reliably don't listen after you go to bed and until you come home from work the next day, why waste tube life on the three-quarters of the day when you are sure you won't be listening? However, if you are always home and often listen at the spur of the moment at any hour of the day or night, it may well be worth it to you to leave the system on continuously.
So, the question is how often you want to replace tubes and also how much electricity you wish to use. Your personal listening style is also a factor. If you reliably don't listen after you go to bed and until you come home from work the next day, why waste tube life on the three-quarters of the day when you are sure you won't be listening? However, if you are always home and often listen at the spur of the moment at any hour of the day or night, it may well be worth it to you to leave the system on continuously.