Although not a basic item, Sorcerer's Shoes is the item from which the flat magic penetration gold value is derived. From this item derives a value of aproximately 34.33 gold per point of magic penetration.
Sorcerer's Shoes is an extremely good item for magic-based champions, as it allows you to ignore 15 of your enemy's magic resistance. Combining these with magic penetrationrunes can be devastating for opponents with low magic resistance.
In contrast, Sorcerer's Shoes is less effective for non-offensive casters such as supports or tanks, as their typically low magic damage stats prevent the item from receiving its full value, compared to the higher damage results of a Carry. One of the two defensive boots would likely be a better pick, as the added survivability will be of more value to these roles.
These boots are less efficient against enemies with high magic resistance. However, they synergize well with other magic penetration items, percentage items such as Void Staff in particular.
For nearly a century, the greatest mage in Valoran resided in the scorched desert of the Zear realm until the first crusade of the Rune Wars devastated the entire region forcing millions to flee. The crusaders killed all desperate travelers attempting the mass exodus from Zear, but one mage escaped their grasp by making such haste across the land that word spread throughout Valoran that the very shoes this mage wore must be imbued with immense power.
Sorcerer's Shoes is the item from which the flat magic penetration gold value is derived. From this item derives a value of aproximately 34.33 gold per point of magic penetration.
Void Staff in particular.
Amplifying Tome in their recipe. In the V1.0.0.52 patch, the ability power bonus was changed to flat magic penetration, and the 
