Re: is lightning strike any use other than being synergy?
Some claim there to be a few situation where it might be more interesting then charged strike or lightning strike. Yet the situations are rare and charged strike and lightning fury will still result in good killing speed.
So no, it's not really useful. The safe way is to always use charged strike and lighting fury as those are always good. If you want, you can experiment with it and find those few situations, yet I don't think it's worth the effort.
So I wouldn't say it's useful, I would say it's less useless then the other synergies.