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I could be wrong, but it seems like the salt water pools are less salty than ocean water, but the pool water is used as an electrolyte in an electrolytic cell which takes water and sodium chloride and produces chlorine gas and sodium hydroxide. The Chlorine gas obviously chlorinates the water like bleach would, but without the increased trouble of having to handle chlorine or sodium hypochlorite. Apparently you do need to dump some HCL into the pool now and again because the pH eventually starts to drop (and that's the sort of thing you want to avoid), and you also have to top up the salt. There'd also be a slight benefit to just having salty water, because it would be a slightly more challenging environment for microorganisms which aren't suited to salty water since the salt could try to pull water out of some.

(Maybe everyone in this conversation already knows all this, but I thought it was pretty interesting and looked it up myself and learned a thing or two and decided to share)