Purpose of "optional":true for beams in vehicle .jbeam

I'm in the process of reorganizing and cleaning up my 1969 Corolla jbeam, trying to preserve the attributes of the beams I am copying and pasting, just wonder if the following argument does anything, and if so what?

ex:
...

["e2r","e4l"],
["e2l","e4r"],

{"optional":true},
{"beamType":"|NORMAL", "beamLongBound":1.0, "beamShortBound":1.0},
{"beamSpring":2001000,"beamDamp":400},
{"beamDeform":30000,"beamStrength":250000},
//engine soft mounts
["e2l","fx1l"],
["e2r","fx1l"],

...