For the science courses, this is totally up to the student and family. Some students find they do best when they read the text first before a lesson. Others like to use the text to study while preparing for the module exam. This lets them skim over what they know well and slow down with material they are still mastering. 

Chemistry is more of a problem-solving type of a course rather than a memorization oriented course. It is usually the first science course students take that is over 50% mathematical in nature. Re-reading is less helpful than practicing the problems to gain mastery over the units that go with each measurement, the equations needed, and how to get organized in tackling the solutions.

There are a few modules where I will teach the content in a different order than the text does. Module 1 has the most significant rearrangement. I move significant digits and scientific notation up in front of the factor-label (unit conversion) topics so students get to practice their significant digit and scientific notation skills on those problems.

Module 2 has a very minor change of introducing the full heat equation from the very beginning instead of waiting until the end. This gives them more time of exposure helping them to memorize the equation easier.

A few modules have key additions the textbook does not have that I highly recommend catching if you tend to read the text instead of watching the lectures. Module 1 has information about how calculators handle order of operation that I find around 60% of incoming students do not realize. that is in lecture 3.

Lecture 2 in module 4 has a valuable workflow for balancing chemical equations that is not in the text.

Module 6 lecture 2 has a critically valuable workflow for solving stoichiometry that has proven to really help students master this skill. Stoichiometry is the most critical concept in general chemistry and will pop up in most of the modules from module 10 on to the end of the text.