Folly said:
The only time I would think this would be useful, is if you do not have easy access to wands and you happen to be a warlock with craft wand. Else either you can buy a new one or you can cast the spell from yours spells.
... or a Bard (small class spell list, and limited spells known, but with UMD, can use a wand of any spell for this), or a Sorcerer (for any sor/wiz spell not on their known list), a magic domain cleric (who can use wands of any Sor/Wiz spell, but can only cast a handful of them), or a Beguiler (who has a sharply limited spell list, but can cast from wands due to UMD), or a Favored Soul (for any Cleric spell not on their known list), or any of the other classes that can use a wand, scroll, staff, or other spell trigger or spell completion item but can't cast the spell directly.
As for the economics, if it takes you one charge to craft a new wand (1st level spells at minimum caster level), you (effectively) get 98% of the wand for 50% of the GP cost of a full wand. If it takes you five charges (for 2nd level spells at minimum caster level) to craft a new wand, you (effectively) get 90% of the wand for 50% of the GP cost of a full wand. If it takes you twelve (3rd level spells at minimum caster level), you (effectively) get 76% of the wand for 50% of the GP cost of a full wand. If it takes you twenty-one (4th level spells at minimum caster level), you (effectively) get 58% of the wand for 50% of the GP cost of a full wand. Except for cases where there's an XP component, an expensive material component, or you're running at a significantly higher caster level than the default (e.g., a 4th level spell at caster level 9), you STILL save GP over purchasing at market price (even if it's not much for the XP burn).
A Wizard will sometimes make scrolls from a spell in a wand, so that it can be scribed into the wizard's spellbook.
Granted, it's generally not worth while for the higher level spells... if you can simply purchase wands. That is not, however, an option in all campaigns.