I have a mixed opinion about drill sheets.
On one hand, I believe drill sheets are slightly underrated. They encourage students to memorise multiplication facts instead of having to derive the answers every time. Although being able to derive answers is an essential skill, it may not be a viable option for each circumstance the student will encounter later in life. Drill sheets help drive students to produce answers quickly. They also motivate students who thrive on competition.
That said, for students who are not yet confident in their multiplication skills, or for students who experience math anxiety or test anxiety, math drills can be a truly agonising experience. The pressure associated with the activity—time pressure, intellectual pressure, and social pressure—often leads to lack of self-confidence and sometimes a negative opinion of math in general, both of which are tragic opposites of good math teachers’ objectives for their students.
In my opinion, drill sheets may be used as a method for learning, but they should not be used for assessment. In other words, I may introduce math drills into my classroom in order to motivate the memorisation of math facts, but I would probably never use the drills’ scores in the calculation of students’ final course grades (it’s possible I may not even collect the drill sheets afterwards). For many students, the pressure of a math drill impairs the brain’s ability to recall stored information; therefore, a math drill may not be an adequate gauge of the student’s ultimate ability to multiply anyway. If I used math drills in class, the purposes would simply be to give students a reason to remember math facts and to provide a way for students to mark their own progress.