These are basically digital versions (like ebooks) of worksheets that can be bought and downloaded to your computer from the internet or from CDs and then printed out. The advantage is that you can print out whichever sheet you wish. If you need to re-inforce a certain concept more you can usually print out that sheet again. Of course you will therefore need to have a computer and a printer.
A homeschooled student will receive the absolute best education possible without the expense and overhead of ordering multiple copies of hardcopy texts. Textbooks will not need to be discarded at the end each school year.
If your third grader needs help with math, there are many useful tools that can downloaded directly from the computer. Math is a subject that is best taught with visual aids, making the lessons more tangible for students.
Homeschool worksheets are a vital part of the student's homeschool experience. They allow the child to test his or her knowledge, and they offer them a practical application for their learning.