What happens when you use vinegar in your washing machine instead of fabric softener?

This is the cheapest cleaning vinegar I could find: - https://amzn.to/44CenzW

I'm using 30mls in a front loader - 5% vinegar is standard; adjust accordingly!

For people that are concerned about damaging machines: The vinegar is roughly @ .4% dilution and is then further neutralised by the detergent residues. If it was neat I'd agree; but not at these concentrations - we're talking 30mls in 8 to 10 litres of rinse water. DOSING is absolutely key here.

I totally understand why people are cautious — vinegar is acidic, and yes, in high concentrations or when used neat it can definitely damage rubber seals, hoses, or metal parts over time. But the key thing here is dilution and exposure time.
In a rinse cycle, I'm using about 30 ml of household vinegar (5% acetic acid) in roughly 8–10 litres of rinse water. That works out to a solution of around 0.4% or less — far weaker than anything that would cause corrosion or damage. On top of that, it mixes with any detergent residues, which tend to be alkaline, so the acidity is partly neutralised.
Many appliance techs see damage from people using neat vinegar regularly or soaking parts directly in it, which is a completely different situation. Used properly, it's essentially acting as a mild pH neutraliser and softener, not a corrosive agent.
As with anything, dosing and common sense are key — more isn't better. If your machine's manufacturer specifically warns against it, then definitely follow that advice, but at the low concentrations used in a rinse, the risk is minimal and the long-term experiences of many users seem to support that.