The most obvious effect of using too much soap in a washing machine is that there will be too much soap for the washing machine to rinse out of clothes effectively. This can result in a residue left on clothes, which may be visible and require the clothes to be washed for a second time.
Machine damage can occur if too much soap is used in a laundry machine, especially with newer, more efficient models. This happens because newer models are designed to use less water and do not need as much soap, but some homeowners still use the same amount of soap. If too much soap is always added to the washing machine, it can build up and clog vital components of the machine's inner workings that will result in the machine breaking down or not working as well.
A buildup of soap in your washing machine can lead to the growth of mold, mildew and bacteria. These organisms will eventually get onto clothes and lead to a smelly machine or clothes, and could aggravate allergies or make people sick.
Using more soap than necessary wastes soap and results in more trips to the store. In order to use the proper amount of soap, read the directions on the bottle of laundry soap carefully and use the measurement lines on the cap to pour out the right amount.