Here's a scenario that many developers have faced: You finish work for the night or whatever, and take advantage of the downtime by running an install of some sort of product that integrates itself within MSDN Help (usually other Microsoft tools or technologies). Presumably its addition sets a dirty bit in the help indicating that the index and search corpus needs to be rebuilt.

The next day you're programming away, and then realize that you need the docs for Xyz. You launch the MSDN Library, to be met by a help update in progress dialog. In recent iterations this can take many minutes to complete (I've timed it at over 15 minutes in some scenarios), during which you have no access to the help, and your PC is overloaded. Generally one doesn't plan downtime around the launching of help, so this is entirely disruptive.

What an annoying oversight. It's pretty clear the indexing should happen during an actual downtime activity (e.g. installing), at the very least as a checkbox option. Back-end loading it like that, as a suprize to be unleashed at the most inconvenient of times, is a very, very poor design decision.