Try some and see what you think.
Old-timers like me remember a time before there was such a thing, and the more grizzled of us will squint at you, direct a stream of tobacky juice into the spittoon and say how a real modeler doesn't need it, etc, etc.
But in all seriousness, it's one of the great developments in kit design, that was made in that time when many of us left the hobby when we graduated high school and focused on girls, beer, military service, etc, and came back later. It does put very nice results within the reach of many more modelers than who might otherwise have to do things like make stanchions and rails for a 1/700 ship model out of stretched sprue.
In that regard, it's akin to aftermarket resin detailing sets ("We used to scratchbuild all that stuff!") or even the ready-made washes and weathering products from vendors like AK Interactive, Mig, and so on. You can try making your own--and in the case of washes or weathering powders, it's not difficult at all--but again, for those who have no experience with it, and even for those of us who do make our it, the commercial products take the guesswork out of it and ensure a certain level of consistency in your results.
I'll add that for ship models, I've come to look on PE rails, if no other PE details, as a necessity for my builds.
But try it, see what you think, and if you find it enhances your fun with the hobby, pursue using it.
Hope that helps, and best regards,
Brad