Old towels are great for potholders and such.
Probably very good for a table runner on the cheap since it’s thin enough to keep glasses from falling over and if you use lofty batting it might shift.
I used to buy ugly old comforters for a couple bucks at the thrift store and gut them for batting.
There are no rules in quilting.
People have always used what they had for centuries.
I have used old mattress protectors, just cut off the elastic, they are batted and quilted themselves.