The CFA syllabus is huge and the CFA Institute books do full justice to the subjects, both in depth and width. For best results in your exam, you are recommended to study the Institute books and practice all the problems and exercises in them.
However, practically it may become extremely difficult to go through each of the 6 odd books of roughly 1000 pages each if you are also simultaneously working or studying elsewhere. Some of the books do get a bit verbose and it can be challenging to cull out the important elements from the not-so-important ones. This is where a guidebook like Schweser can help you.
It is always better for a student to go by the CFA Institute material if there is no time crunch. Those books explain every concept in great detail and almost always start with basics. Schweser notes can become challenging as they serve to exclude few explanations. They will help you clear the test but won’t help out students in clearing their concepts. Students can definitely refer Schweser materials but along with the Institute books would make it much more easier for you to clear your exams.
Scores of candidates have used Schweser materials along with the Institute books as a guide.
Schweser books should be used as a supplement and not as a replacement for or a shortcut to the CFA Institute books. If you are really short of time, you could use Schweser books alone for 1 or 2 Study Sessions at the most.
NOTE: The topics in Level 1 that you should definitely NOT depend just on guidebooks
• Ethical and Professional Standards
• Financial Reporting and Analysis
The above 2 topics together alone constitute ~35% of the exam content and cannot be taken lightly. Ethics especially is not very well covered in any coaching book and is best studied from the CFA Institute book.