Leaders surely did so, primarily to increase fighting spirit of their troops - not only because of the motivational effect of the speech itself, but also because of showing their own active participation to their troops. A leader advancing forward with their army was considered a noble and courageous man and thus people were more willing to endure hardships if they knew they leader would do the same for them.

There are some surviving documented battle or pre-battle speeches. For example, during 1253 joint allied invasion of Austria and Silesia conducted by coalition of states with Hungary at its head. Combined Rus-Polish army's vanguard near Czech city of Opawa was surprise attacked and defeated by the garrison. In order to strengthen his allies' resolve for the hardships of incoming campaign after this failure, prince Daniil of Galich, leader of the Rus forces, told them (my translation can be a bit rocky):

"Why are you afraid? Don't you know there is no war without the dead? Don't you know you're dealing with men and warriors, not women? If a man dies during a war, what kind of surprise is that? Many die at their homes with no glory while these people did so with glory. Steady your heart and rise your weapon against your enemies!"