As more and more creatures with enter the battlefield effects, low costed high toughness, or mana taxing abilities have been printed, the one-for-one trade that Lightning Bolt offers has become less and less appealing
Felidar Guardian is a 4 mana 1/4 which flickers another permanent when it enters the battlefield
Always netting you one permanent, this creature synergizes in incredible fashion with artifacts that provide benefits when they leave the battlefield such as Ichor Wellspring and artifacts that can recover other artifacts from the graveyard such as Myr Retriever
The idea is that at individual scales the additional load is ignorable, but at mass scraper levels it adds up and makes scraping much more expensive
Ive just put together different cards you might want to play in your sideboard to have a toolbox of sorts
Sure, the card is powerful and will be great in Commander, but its hardly an auto-include within every deck