What kind of a douche rinses with vinegar and water?
No, seriously, what the purpose?
Well, it depends- how dirty are your clothes? How important is it to have your whites whiter?
Fabric softener but without the leftover residue that can cut down on towel absorbency.
Vinegar will also remove any DETERGENT residue that can irritate some people’s skin.
It rinses cleanly, leaving no vinegar scent. It’s cheap, and it’s usually on hand.
Vinegar is also good for cleaning mineral deposits out of either the washer or the dishwasher.
~VOW
Which is the effect of perspiration. It doesn’t matter which detergent you use for that; you have to pre-treat it. I’ve found that Folex works best, which is actually an industrial carpet stain remover.
This. fabric softener works by leaving a “coating” on fibers, which isn’t something you’d want for towels.
Yeah - the residue is wax, which, of course, keeps clothing from building up a static charge, because it acts as a lubricant, but it also keeps towels from being as absorbent as you’d like them to be. Vinegar is simply very weak acid, which dissolves the wax.
Using Vinegar also eliminates the smell of mildew from towels that were left in a washer too long.
Women have, in the days before Summer’s Eve, traditionally douched their lady parts with vinegar and water.
No kidding. Was my intended joke that subtle? 
A lot depends on the water too. If your water is hard (like supplied from ground aquifers) then the detergent has to “work more” and a good detergent will contain good water softeners. With water that is not hard (usually from surface reservoirs or rivers) the detergent does not make a lot of difference.
If your clothes are coming out not soft or if you notice deposits in your shower/tub - it usually indicates hard water. A shower under hard water will also leave your hair feeling dry - you typically use less less soap while showering with soft water.
I got it. And I’m a dude.
Until my wife and I had a child, it really didn’t make much difference what detergent we used- typically, I think it was All Free & Clear, since she doesn’t like scented detergents and it was cheap in bulk at Big Lots.
Now that we have a toddler, the performance of the detergent has become much more important, since they get food and grime in places you wouldn’t think possible.
It appears to me that the majority of detergents are about equal in general detergency, but that the real differences come in the cleaning and stain removal enzymes (and quantities thereof) that are part of each particular detergent.
For example, the unscented Tide and Wisk detergents are noticeably better on baby and toddler clothes than the unscented All or Purex detergents. (in particular on formula and breast milk residue).