Channel grouping matters if you have multiple servo's controlling one surface, or two or more servo's on the elvator etc: as far as I can remember the 2.4Ghz grouping is in three's 1,2,3...4,5,6 ect so you would not want a two elevator airframe operating the two servo's on channels 2 & 5, I think the channel assignements within the Tx do this automatically.

Mike