The importance of quality over quantity applies to so much more than just one aspect in health and fitness, whether it's training, nutrition or life in general. Let me break it down section by section.
Quality over quantity with training - so for example say you are doing a dumbbell bicep curl, you are using a 20kg dumbbell and after 4 reps you swing it up arching your back, your shoulders are assisting, how effective do you think your biceps are working ???,. I can tell you, not very and training this way may make some gains, but not as much as if you are properly lengthening and shortening the muscle using a mechanically suitable load (not too heavy for YOUR ability to perform the exercise) then use tempo and volume as the tools to create fatigue and damage. Take it from someone who knows, I ego lifted for a while and all I got was sore joints, crappy form and lost time from making true progress. The amount of people that focus and obsess over "lifting heavy"! The thing is - what's heavy to you could be light to someone else or what's light to you could be very heavy to someone else and depending on what outcome you are after from bodybuilding, power lifting or strong man, all these disciplines use different structures, rep ranges and exercises, the typical rep ranges are 1-6reps for strength, 6-15reps for hypertrophy, 15+ for endurance, but even these can vary from person to person. It's a case of trial and error and figuring out what works for YOUR body.
Quality over quantity where food is concerned is just as important as training, maybe more so, so consider this - you have heard the saying "you are what you eat" which is true to a point, but what's even more to the point is you are what your food eats, so take most farmed cattle and farmed, both are pellet fed with a high influx of antibiotics, this is to reduce health issues with the animals and increase the yield of the product for the farmer or company, with this influx of antibiotics it can have an effect on your ability to digest food, as antibiotics kill bacteria indiscriminatly whether it's bad or good, so the millions upon millions of bacteria you have in your gut to help break down and digest the food you eat and maintain general gut health can be affected to the point where it can create food intolerances. A lot off pigs are fed food that's extremely poor quality (raw sewerage) this also can have a knock on effect to the people that consume it's meat, so by eating food that is higher quality, not just in reduced chemicals or pesticides, but by the animal itself having a higher standard of food, in a lot of cases it will help your intake of the nutrition from those foods more than the poorer versions, so you can eat less and have the same or greater nutritional benefit. Forexample 1kg of poor quality mince beef a day is probably around the same value as 700g of free range steak mince, yes there is a price difference but with the reduced amount of volume of food needed it's a very small cost difference. Personally I put my health and nutrition above all else as I feel a huge benefit, not just energy wise, but in recovery and sleep. My skin, mood and thought process all feel heightened when eating high quality healthy food, so regardless of whether you're an omnivore, vegetarian or vegan, always look for better quality not just a bargain.
So next time you think about throwing a dumbbell about with crappy form or buying food a bit cheaper, think whether it's wasting your time or doing more harm than good, don't be cheap or ego driven, take your time, do it right and gain the benefits form your hard work and dedication 💪