Theres no way to figure out what will happen or what the optimum amount of detergent is because it can depend on a lot of things like the fabric (type, color), type of stain (oil, dirt, paint, ink etc), detergent formulation, washing machine, water (minerals/tds and temp) etc. The worst that can happen is permanent stains on your clothes but that can sometimes happen even if you use the right amount. You clothes might also not smell as strongly of detergent but that doesnt mean they arent clean.
Theres no way to figure out what will happen or what the optimum amount of detergent is because it can depend on a lot of things like the fabric (type, color), type of stain (oil, dirt, paint, ink etc), detergent formulation, washing machine, water (minerals/tds and temp) etc. The worst that can happen is permanent stains on your clothes but that can sometimes happen even if you use the right amount. You clothes might also not smell as strongly of detergent but that doesnt mean they arent clean.