In this episode the customers browned out the carpet with too much soap. ( bissell machine).
Not rinsing will leave a soapy residue. Over time it browns out. Too high on the PH Scale. If rinsed it would have neutralized the high ph alkalinity down to neutral 7 and looked fine afterwards.
source
Rinsing with vinegar after a bissell cleaning keeps residue at bay!!
Looks great!!!