As Faster say's, a lot depends on the boat. On my 21' Cal they would be particularly inconvenient if installed. The stanchions would be tripping you up more than any safety benefit derived from the lifelines. In my opinion, you are much more likely to be hurt by tripping than you are to be saved by the lifelines. As stated, for them to do much good you'd have to already be off your feet. Given that most lifelines are located well below your center of gravity, it is not like they are holding you on board. You're more likely to grab them on your way overboard than anything else. How well they perform at that time is dependant upon the quality of initial installation and subsequent maintenance. Given the below deck construction of most boats, how often do those stanchions get re-bedded?
Once again, I am finding myself in agreement with the Dog. Why not install something that works? Something that has a much greater potential to keep you on board versus clinging to the side. A well thought out set of jacklines coupled with an adjustable harness should be a higher priority than lifelines. That system will actually aid you when things get nasty.
I'm not sure that I'd remove lifelines already installed, unless they are a hindrance to mobility, and many can be. They certainly are an aid to containing adrift sails. This is certainly a subject that one cannot make any hard and fast statements on as it must depend upon the boat and her intended use.
“Scientists are people who build the Brooklyn Bridge and then buy it.”
Wm. F. Buckley, Jr.