It can be a lot of discussion as to whether the sheath affects the sound, and if so, in what way. Personally, I like the sound of the Elixirsaiten - regardless of whether he is affected by the said by the company "Nanoweb" tissue. If the strings are new, not one notices this jacket really. However, if the strings get old, they start to peel off, especially in places that you worked with the plectrum. This can interfere with - however the sheath holds quite a long - depending on Bespielung.
I just like it when the strings to rust as late as possible. I have more than one guitar, and so it is possible that a guitar once a long time is, without being played. Since it comes in handy when the strings are preserved.
If you anyway once a week, the strings will change, but the extra expense is inappropriate here.