If you use more than than is suggested, it won’t get rinsed out of the clothes or the machine. The excess detergent will settle in the clothes and in the washer. If you continue to use more than suggested, eventually your washer and your clothes with have a nasty smell. Not only will your clothes smell, they will look dingy. You might develope an itchy rash from all the soap that has built up in your clothes.
If you know what bathtub scum is, the washer will have a similar build up. Your washer always holds water that you don’t see. Some hold several gallons. This help the seals and hoses from drying out. The excess detergent will settle inside the washer in areas you can’t see. This scum is nasty. It’s smelly, sticky and thick. It’s actually the byproduct of all the chemicals in the detergent, along will all the dirt, bacteria, and nastyness that’s been in the washer. This scum is not easily removed. It has to be scrubbed off. And to scrub it off you have to disassemble your washer.
It’s best to follow the directions and do what the detergent companies suggest. After all, they developed the detergent, they know what it does, you don’t.
Btw, this is true for all cleaning solutions and especially floor cleaning detergents. Less is always best. Using more that suggested will dull your floor. It will look slimy. It will also be a safety hazard. Built up detergent on a floor is like pouring oil on the floor. Someone will get hurt.