Hi, my name is Emos and I am a Key Hoarder.
In all seriousness I do save all of my keys for the appropriate times, mostly to obtain a new Mythic. It helps immensely that I have the troops I need for the end game so I can stockpile. I’ll run out of some Runics at times until I go on another Key opening spree.
For Mythics I go in the following order until I hit: Guild, Glory, Gem, VIP.
Event Keys I do the following: For a new Legendary in an old kingdom I’ll usually just open enough to get one or two copies because there’s other old Legendaries that dilute the pool. If it’s a new Kingdom event I’ll go all out until I get enough copies to Mythic the new Legendary, especially if it’s awesome.
Gold Keys I now wait until a new Kingdom arrives then spend an hour or so opening them ALL to get the new Common and Rares ascended to Mythic hopefully.