The following is an excerpt from the same document that was mentioned in the previous post. But I decided to include it in this post, because there is one issue, which concerns the focusing in AI Servo AF Mode - first frame could out of focus. So there is a good reason not to shoot single shots in this mode. And below is the explanation of such behavior:

"There are two issues at stake here: the first is focus tracking and the second is a phenomenon known as “release-time lag” or “shutter lag.” In One-Shot AF, pressing the shutter button halfway locks the focus. When the camera is set for AI Servo AF and the shutter button is pressed halfway, the AF system begins tracking the subject. If you simply press the shutter button down without waiting for the AF to function, the shutter release might lock up or be delayed in One-Shot AF. Under the same conditions, the shutter will release without focusing in AI Servo AF. This is true with or without the use of an AF-Assist beam. Conversely, pressing the shutter button halfway and holding it there until you are ready to shoot allows the focusing system to lock focus in One-Shot AF or start tracking the subject in AI Servo AF. Pressing the shutter button down all the way once focusing has been established will release the shutter in the shortest possible time, thereby increasing the odds of capturing “the decisive moment.”