Practice makes perfect. Learning math requires repetition that is used to memorize concepts and solutions. Studying with math worksheets can provide them that opportunity; Math worksheets can enhance their math skills by providing them with constant practice. Working with this tool and answering questions on the worksheets increases their ability to focus on the areas they are weaker in. Math worksheets provide your kids' the opportunity to analytical use problem solving skills developed through the practice tests that these math worksheets simulate.
I will admit that there is one type of worksheet that I used in the past and found relatively beneficial, although it had a different kind of flaw. For my Basic Math, Pre_Algebra, and Algebra classes, I had several books of "self_checking" worksheets. These worksheets had puns or puzzle questions at the top, and as the students worked the problems they were given some kind of code for choosing a letter to match that answer. If they worked the problems correctly, the letters eventually answered the pun or riddle. Students enjoyed these worksheets, but there are a couple problem areas even with these worksheets. Some students would get the answer to the riddle early and then work backward from letter to problem answer, so they weren't learning or practicing anything.