Both lower_level_thinking worksheets and too many (even high quality) worksheets can hold students back by not providing stimulus and challenge. Studies have shown for years (just do a Google search!) that children learn best through active involvement and real_life experiences. Virtually every teacher knows that children learn to read by being exposed to books and by being read to, NOT by completing worksheets. The same applies to all areas of learning.
As far as using worksheets for busy work, the verdict is in. It is destructive to classroom learning to assign worksheets to simply keep students occupied. Busy work creates monotony, causes boredom and increases the likelihood of behavior problems. To know if you are on the right track with worksheets in your classroom, answer (honestly) these simple questions: Do my students groan when I hand out a worksheet? (The answer should be no.) Are my lesson plans based on worksheets? (The answer should be no.) Do I feel anxiety if I don't have worksheets copied? (The answer should be no.) Are students excited about learning in my classroom? (The answer should be yes!).