How important is it to have air cushions and/or water hammer arrestors in plumbing? My current galvanized plumbing has some sections of pipe where there is a long straight section coming off a "T" that simply ends in a cap. My assumption is that is an air cushion for preventing water hammer. Is something like this normally necessary if you do not have excessively high water pressure? Is something like this valuable is catching dirt, sediments, whatever in the pipes and preventing clogging of the fixtures and aerators?
Since I'm going to be installing PEX I'm not terribly concerned with water hammer, but what about putting sediment traps in the lines? Would it a good idea to do this, or are there better ways to filter out city water refuse?