In high bather-load pools, such as many commercial/public pools, even having higher chlorine levels isn't enough to keep up with the bather load, especially in indoor pools where there is no sunlight (so no UV) to help break it down and the air circulation is often poor. In these situations, supplemental oxidation is helpful such as from UV or ozone systems or from use of non-chlorine shock (MPS) or enzymes. This isn't necessary in a residential outdoor pool since the bather-load is so much lower so chlorine is able to keep up.
Also, in indoor pools, Cyanuric Acid (CYA) is often not used and this makes the active chlorine (hypochlorous acid) level higher by a factor of 10 or more. This can lead to much higher concentrations of volatile and very smelly and irritating nitrogen trichloride. It's a delicate balance -- if one uses too little chlorine in absolute (FC) terms so that it runs out, then one can end up with too much monochloramine which is associated with "pool smell" though not quite as irritating while if one doesn't use CYA then one can end up with too much nitrogen trichloride.