In my deck steal is 1 in 40 precisely BECAUSE it is situational.
Against Gemini I use it to either steal lobo or gravity tower (both are essential since early lobo will effectively stop ALL of his momentum, while having a quinted oty by turn 3 is an automatic win, something you usually can't afford with just QT though)
Again Fire Queen I used it to steal ferral bond, this allows me to survive even while my shields are down and pretty much guarantees an EM if I win (with 20 creatures I heal by 40HP, which is VERY nice)
Against Elidnis and Scropio it is UBER useful if you steal the aether tower early, or to steal a weapon (say the nasty arsenic) if the card is later on
Against Morte stealing Arsenic is often what saves me from being poisoned to death
Against Incarnate you more or less HAVE TO steal his boneyard if you don't want to be overwhlemed by his skellies.
Paradox/Rainbow/Destiny I like to steal their hourglass
Miracle.. I like to steal his early emerald tower since it prevents him to FF spam and also helps me get my own queen/druid combo going active... Later in the game I usually steal light tower in an attempt to slow down his miracle wall.
Chaos Lord, I always save my steal until I have 100+ damage worth from creatures and then I steal his dissapation shield and bam!, he is down to 50 HP
Other gods, other uses... but as you use, you generally DON'T need many steals, but against every god you need like ONE or TWO.. this is why I chose to have one and to use it situationally... Steal is often NOT a clear game changer, but it is also VERY useful and it is often a FREE card (since no other dark quanta are used in my and most other FG grinder decks).