I just farmed the 80 shards from GW. I usually activate right away but I guess it's a ..."waste?" if I pull him from Brozium (whatever) card. What are the chances of THAT though? 270 million to 1 and...
you can always activate later and keep saving shards.. Might be safer then sorry, no point of having a 5 star character and getting extremely lucky and pulling what could have been extra 80 shards.