A prefilter isn't strictly necessary. In fact, many people prefer to skip the pre purifier altogether.
But if you do decide to add one, make sure it has a high-quality rating.
Some people do like to use prefilters because they can actually be pretty helpful.
After all, they'll reduce the amount of sediment that gets into your purifier.
This means that your primary filter will last a lot longer than usual.
Plus, they make the purifier run smoother. A prefilter is especially beneficial if you're going to use the purifier in areas where there's a lot of debris.