I am using a liquid detergent and I use exactly the half of the detergent they say I should use. If a the washing machine requires 1 cup, I do half. Mostly because I don’t trust the company to put me over their interests.
Now, what will happen? Will my clothes end up staying dirty? Will it not remove stains which a full cup would have removed? Will surfexcel kidnap me and torture me for not obeying their commands? Help meeee!!
Typically one trusts the instructions, but it does depend on the kind and quality of detergent, the quality of the machine, and the amount and types of clothes. I myself just entered an era of having no working machines for two days (on my third and am surviving on a pink hoodie over purple plaid shirt, jeans, and temple garment bra/panties which is my “last life”) because the slots are broken on both home and public machines and do a half-effective job.