BritishStorm, I use vinegar for my towels. I once heard that softener doesn't actually do your washing any favours. I haven't bothered looking that up to confirm it, but I prefer vinegar because it's simpler. LOL.
Never. It is bad for washing machines so I use vinegar as a rinse aid as advised by washing machine repair person years ago. Vinegar also removes any left over washing powder from the clothes as it is an anti-sudsing agent.
I use it only for my towels. I have used vinegar but found it doesn't soften the towels like the fabric softener does. Once in a while I give the washing machine a cycle containing washing soda only (no clothes) which is also something washing machine manufacturers used to recommend years ago.
I used to use softener when I was washing and spinning my llama wool however as I havent done this for some time, I do not use softener.
I was told it is not good for towels as they do not dry well if you use it.