Let the chems do the heavy lifting. Enzyme presprays are my favorite. Lay it on heavy so it stays damp for about 20 minutes, then go at it. Grease isn't even close to a challenge if your chems are on par.Kind of inline with what your saying in my very early experience cleaning carpet I feel largely that the chems are doing most of the work. Its crazy to see them go on and the carpet start to look better already. Of course, we perform a lot of labor after the chems but to me they are doing most of the cleaning.
Maybe some others feel this way as well..
Then I think every carpet cleaner has their own secret mix of "carpet nuke" when the customer doesn't care about anything and it's a "good results or we replace it anyway" kind of job.