It's often easy to lose track of what you're doing, especially if you have a busy day full of meetings and rushing around, it can often be easy to sign off and not think about tomorrow until you have to. But what if you're not coming in to the office the next day? You might be booked in to work at a client site first thing in the morning.
For this reason, it's a good idea to end each day by having a quick glance at your calendar. If you're especially busy, it can also be a good idea to have a paper printout of your week so you can look at your appointments in the car or on the move.