If you have a degree in finance or accounting, you can use schweser 95% of the time and use CFAI materials for more background on subjects you're not that familiar with.
If you don't have a STRONG background in finance, you'll want to spend the extra time reading CFAI books. At least 40 - 50% of the time.
The thing with Schweser is it will condense a paragraph or two into one sentence. If you're not already familiar with the underlying concepts, will you really remember this one sentence 6 months from now? Probably not, it would be much better for you to read the two paragraphs and UNDERSTAND what it means.
If you have the time, read CFAI first, then read Schweser (Book 1 CFAI, then Book 1 Schweser, then Book 2 CFAI followed by Book 2 Schweser.... etc etc) You'll get the underlying concepts, and then an extra reinforcement of the important topics.