Long-time practice picked up from my grandma. When we cook a roast, we always save the fat - dripping - and re-use for the next roast, or roast potatoes, or to make roux for gravy.
Recently discussing fatbergs with friends, all agreeing how yucky it is that people pour fat down the sink. I said that we save fat and put it in the fridge so it solidifies. My friends looked at me, aghast, and one said, ‘but surely just to make it easier to throw away, you can’t possibly use it...’. I gave a non-committal response, but am now not sure if we’re being thrifty or whether this is a disgusting practice.
(FWIW, the dripping makes the best roast potatoes).