Grafting would be useful to me when I want to speed up experimental plantings of newly found interesting specimens. From a cutting I would get some flower and fruit in the 3rd year. If I could get a graft onto an established root then I could in theory get the flower and fruit in the 2nd year.Not too sure why you would want to graft elder but there is an easy way to get new elder plants, just pull off the complete little tufts that sprout from dry stems and pot them.
Once they have grown to garden planting size , plant 2 or 3 different kinds close together in a clump
Tant
Also I have come across a couple of specimens I was interested in that just refused to root for me (after several tries at different times of the year, so again if I could graft then I might be able to propagate them more successfully.