How young/old are you? Sure, you can sleep on total crap when you're 18; when you are 40+, not so much. You'll damage a lot and might have serious problems later on in life. This goes for a lot of things. If you keep wearing flip-flops into your 40s, you'll probably get serious back, knee and hip problems. Good (and usually they are expensive) footwear is a must if you care about your body. So is a good night sleep on a well developed bed, if probably a medical bed (not sure what the English word is; in Germany tons of hotels have them and that made me buy one, in my 20s, i've never looked back), at any age (and those are expensive).

But if you don't care about the future, then sure; it's your life. But maybe you just never thought about this.

Edit: changed some 'will' into 'might'; some people just are unbreakable. Most of us are not though although we think so when nothing ever happened so far.

Edit: another good example is an office chair or standing table; just SPEND the money on really good desks and chairs; it's just plain stupid not to.