Wayner, in seasonal pools, there is a bi annual drawdown of pool water; one in the autumn and another in the Spring, which dilutes the calcium hardness acquired through cal hypo additions over the previous swimming season. As pointed out by others here, prolonged use of cal hypo with no seasonal water replacement leads to elevated hardness and the possibility of scaling, so liquid chlorine is preferred. SWCG is perhaps more 'maintenance-free', during routine chlorination, but I don't see too many advantages due to our short swimming season, compared to SWCG running year round.