This is about accomodating the relatively recent “fairy light” type controllable pixels, with each pixel being a bead or blob along a cable (typically 3 thin solid wires with super thin insulation or three flexible wires in transparent flat cable). In these, all pixels receive data in parallel (the data line is continuous from start to end rather than being daisychained through each pixel), and each pixel has a preprogrammed offset (how many 3 byte groups to skip before accepting data). They tend to come in 3m, 5m, 10m and 20m lengths, with 10 pixels per meter (there are some alternative spacings).
I like this physical format, which fits well into some things like small ornaments, so I cut sections from a longer string. A given prop might have (0 indexed) pixels 150 to 199. To send to it, I would need to sent data for 200 pixels, of which only the last 50 are used.
Using WLED standalone this is not a big problem; I can use a dummy segment for the first 150. The problem occurs in using Artnet or E1.31, where I would need to send two universes to control 50 pixels, because those protocols go to all pixels, not just one segment. That is, I have to send 200 pixels of data OTA.
If instead of “Skip first pixel” there were a configuration for “Skip first [ ] pixels”, I could just skip the first 150 pixels, as if they were sacrificial pixels and WLED would treat my situation as just having 50 pixels.
On a possibly related question - in the e1.31 configuration section, there is an option for “Realtime LED offset”, but I cannot find documentation on what that does. Perhaps it would solve my probem? Would I use a positive or negative offset if so?