Handouts can increase the speed of a lecture to a pace at which students cannot follow. This use of handouts to arbitrarily increase the lecture content is unsatisfactory. Difficult algebra where it is important to get every step right. This should not be an excuse for a rushed explanation of difficult material. Handouts are not useful when used in a manner which encourages a class to become bored and fall asleep.
Some lecturers prepare handouts with gaps for the students to fill in during the lecture.
Where this is done, it is important to show clearly what students are expected to write. It can be difficult to follow a lecture and work out which gaps need to be filled in at the same time. It is helpful to include notes in handouts to indicate which Examples papers can usefully be attempted at each stage of the course. The number of handouts is not important if they are used properly. They should be clearly labelled to show their sequence so they can be easily arranged in the correct order.