The choice of including and excluding or using less friction also depends on the fluid service for which the equipment (Static & Rotating) is used. For example, water service of ambient temperature condition, where the leakage cause less harm, the routing can be simple and not to be complicated with much flexibility in piping. For those cases, the advantage of PTFE (mu = 0.1) can be taken.

As Mr.Richard Ay said that mu decreases with time - it is also the responsible of the operation team to check the supports such as spring hanger, PTFE pad specially provided for pump nozzle loads during the pump maintenance or shutdown time etc...

So from my point of view, the effect of PTFE can be taken for a less harm services and low temperature and pressure services....