I get to speak to a lot of large companies about why they install wireless networks and here are the three best reasons I've heard:
1. Cost of building out new office space - when a company is growing and acquiring more room for the employees the "cost" of deploying a wired network is a lot more expensive than wireless. This includes cabling, switching and time (most important).
2. Security - for large organizations it is too cost prohibitive to move to 802.1x on their wired network. With wireless this is built into the standard. Enterprises see adding wireless as a way to make their networks more secure, not less.
3. Flexibility (you call it convenience). Most companies move people and assets all the time and with wired infrastructure it becomes way too cumbersome.

If you want more details http://www.airwave.com/airwaves/2007/09/25/a-real-business-case-for-the-all-wireless-office/