[L]eaders must consult with others, building alignment of purpose through the hard, delicate, necessary work of careful consensus building.
-- Bob Lewis
"IT alignment" is business-speak for having an IT department that supports strategic business goals as the top priority over departmental goals. In my personal experience, this often boils down to supporting financial or sales objectives over sustainable IT infrastructure, but your mileage may certainly vary.
Many organizations seem to have an adversarial relationship with IT. Some of this may be because IT is often a cost center rather than a profit center, while some of it may simply be because keeping the servers running or the firewall tight is a different mission than that of the sales department.
Real alignment is when multiple departments share a common vision. Weasel-speak alignment is when the CFO directs the IT Director to poke holes in the corporate firewall so that Joe in sales can access his one-off desktop database from the field rather than using approved, secured, and managed corporate applications such as the company's PostgreSQL database.
I couldn't find a source that talked about over-alignment. Perhaps you'd like to provide us one for proper context.
With that said, the CIO, CTO, and other IT executives have a core responsibility that isn't just to say "yes" to the rest of the organization. IT exists to support the business mission, but it is also generally responsible for systems security and stability. This occasionally involves saying "no" to something that would compromise the mission, or offering alternative technical solutions for a business objective.
Mordac, the Preventer of Information Services is a great example of what can happen when IT is not aligned with the business. However, over-alignment is also possible. For example, replacing a reliable Linux server farm with the new Windows 2032 Greed Edition (blowing IT's software, training, and labor budget in the process) because someone on Mahogany Row saw an article about it in a magazine is another Dilbertism, and a great (if admittedly contrived) example of over-alignment.