The crap work you offer in exchange for crap fees will ultimately crap on you.
Good, Fast and Cheap. You can have any two, but not all three. Or so the design industry guru types say. It's an old standard, a design industry dogma, that you're going to hear many times before you're done art school or after you've watched a few designer talks.
You can have good and fast, but it won't be cheap.
You can have good and cheap, but it won't be fast.
You can have fast and cheap, but it won't be good.
The logic of the first is that if you pay me enough, I'll do good work and turn it around in short order, prioritizing it above all other projects. I'm able to afford the sudden shift in priorities and the risks this entails because of the higher compensation.
The logic of the second is that if you can wait longer than usual, I'll do good work and not charge you as much for it. I'm able to put the time in for something good at a discount because I'll fit the job in the free time I have between other jobs. I don't have to prioritize it above others, so it's less of a hit to my schedule and cashflow.
The logic of the third is that you can have the work done quickly and affordably, but it won't be of very high quality. Because you're not paying me a lot, but you also need it quickly, I will by necessity rush it and ignore certain details, prioritizing a form of functionality over any nuance or beauty.
I think some call this aphorism the Designer's Holy Triangle. I don't like that name very much, but let's just go with that for now. While I think there is a lot of truth behind this law, it's not actually very helpful in the long run. Yes, for rush jobs I charge more, and for jobs that will be really really good, I estimate that they will take a lot more time and require higher fees in return. But in reality, nobody wants to produce crap work, and if you're anything like me, it's almost impossible to deliberately do something of inferior quality.
One thing I dread is making stuff that I will later regret. It is almost always the case that I regret something about my work after I'm done. But I can at least stand by the fact that I tried my hardest. My work is precious to me, and I care about what happens to it when it goes out into the world. I don't ever want to see something I intentionally made crappy on Pinterest — or any other place — with my name on it.
I believe that making crappy work for any reason will only hurt your image in the long run. You may not show it on your portfolio, but Google might show it in an image search. Whatever happens, that thing you made because you took on a job you actually didn't want will be seen by others, and some will know who did it. And that's something you can't afford in the absence of infinite time and attention.
You may not love everything you've ever created. But you will not grow by creating deliberately crap work due to a budget. The choice is yours — choose to make good things and find other ways of leveraging the compromise. Maybe the client won't pay for a rush job, but perhaps they will give you other benefits. Perhaps they'll include your name in the credits even though they weren't intending on having credits at all. Maybe they'll mention you or blog about you. Who knows — look for a way to sweeten the deal for both of you. But don't make crappy work, not for you nor anybody else. Your time is limited, and so is other's attention. If they see only your crappiest work, or even just one crappy piece, that will speak louder than you might want or expect.
If anything, the "Designer's Holy Triangle" is pretty passive aggressive and reeks of entitlement. I've never heard this good-fast-cheap axiom spoken out of goodwill toward the client. Like people who declare themselves as "taxpayers" in a sentence*, the sentiment often comes with a whiny, holier-than-thou sense of entitlement.
Should you find yourself faced with the choice to do fast and cheap work, you probably don't actually want it. It makes no sense to take on work that will drain your creative energies and steal time from your more profitable jobs. It also makes no sense to have to explain to your client that you're going to do a crap job for them because of their crap budget. If in fact you do want to take on a champagne job on a beer budget, you probably see it as a good opportunity and a worthwhile sacrifice of your blood, sweat and tears. In such a case, playing by the good-fast-cheap rule would be self-sabotage.
Granted, there may be varying degrees of good in your service and product. There may be some features that come at a premium. But your name goes on every thing you produce, and you want to be sure that all are worthy of your logo — your seal of approval. When you go to buy a car, you don't expect to get a Lexus at a Toyota price, but you know both are good quality products with favourable reputations. A client may not be getting the Lexus version of your work, but the "Toyota" they drive off the lot will still be a vehicle of your reputation and brand. You should always be able to stand behind your product. You and your clients should be able to confidently declare that you do not make crap work. Because not good is not an option.