Does it really matter when you read your mail?

So I'm reading a new book that has been pretty interesting so far. Its called, "Never Check E-Mail In the Morning". We recently had an internal speaker at a meeting that spoke about how to master how you plan the day and as a result control more of how you spend your day.

I've been trying to block portions of the day for certain activities and it really does seem to make a difference. The theory is that for the time you save moving from one activity to another, you loose a lot of time trying to figure out what you were just doing.