How long to leave out dry food?

Should I throw out the day old dry food that they didn't eat from the day before, each day? I have been just adding new food to the bowl each morning. Sometimes they don't seem to eat as much. Maybe I should throw out any leftovers, wipe out the bowl and put new dry food in each day. However, I hate to waste food if it isn't necessary. It kind of seems to change smell when it's been out of the bag for a day or so. But, if you use one of those big feeders, doesn't the dry food basically sit "out", for days?
What do you think.

I think that like anything else, it gets stale. Try putting a smaller amount in the bowl and instead of wiping it out, wash it thoroughly.

I only place enough dry food in the bowl that I expect the cats will consume withiin a certain amount of time. I feed my cats in the morning and in the evening. Their food isn't sitting out for more than 12 hours at any given time.

I used to change out the bowl every 24-48 hours but Zoey is a dry food addict.. I now fill it twice a day

I'm in favor of replacing and washing daily.

I think that is best to wash our cats food & water bowls daily. I store unused food tightly sealed in the original bag. I place that bag in a plastic bag & seal it so no oxygen gets in. I replace their food & water evey 12 hrs.

I pour new bags of food into sealed containers and fill the bowls each morning. If there is some left in their bowls in the morning, I dump it back into the bin, wipe the bowls clean then refill. Any food going back into the bowls is 99% fresh and I'm not wasting any food. Since I refill their bins once a week, any recycled food never really gets stale.

Probably not the optimal approach, but does save me a little money.

When I change out the old food, I put it in an outdoor pet feeder so the stray cats can eat it.

Stale food is better than no food at all.