The Wish spell is a more potent version of a Limited Wish. If it is used to alter reality with respect to damage sustained by a party, to bring a dead creature to life, or to escape from a difficult situation by lifting the spellcaster (and his party) from one place to another, it will not cause the wizard any disability. Other forms of wishes, however, cause the spellcaster to weaken (-3 on Strength) and require 2d4 days of bed rest due to the stresses the wish places upon time, space, and his body. Regardless of what is wished for, the exact terminology of the wish spell is likely to be carried out. Casting a wish spell ages the caster five years.
Discretionary power of the DM is necessary in order to maintain game balance. For example, wishing another creature dead is grossly unfair; the DM might well advance the spellcaster to a future period in which the creature is no longer alive, effectively putting the wishing character out of the campaign.