This is a card to cross your fingers and toes for - I particularly like the art for this one: that certainly is a vampiric tutor
Too few lands and the player will have great hands full of spells but no land with which to bring them in to play (this is known as being "mana screwed") whilst too many lands means the player is able to play lots of spells but their chances of drawing them is lessened (this is known as being "mana flooded.") This is further compounded by the effectiveness (or power) of a card being designed to correlate with its mana cost (or how many lands must be used to cast the spell)
Lastly, make sure your theft deck has lots of ramp
The term Aristocrats is derived from the cards Cartel Aristocrat, Indulgent Aristocrat, Vampire Aristocrat and Falkenrath Aristocrat that have these types of abilities and Aristocrat as part of their card name
In constructed it may have applications because its an instant
But with Heart of a Duelist in play, if you believe that the card you need to draw is the ninth card from the top, you can draw that card instead of the one that's on top of your library