I make up a litre bottle of fixer for films only. I use and reuse it, but note down the number of films done until I reach the manufacturers recommended limit. I store it in a concertina bottle, and squeeze it down to exclude air before putting the lid on. I do the same with a chemical stop bath. It's only necessary to avoid a chemical stop for certain films with delicate emulsions. Otherwise, I believe it prolongs the fixer life. Generally, I have the stop and fix ready to go and only have to prepare the developer to get going. This saves a lot of time( and money!).