The US Department of Education's Office of Educational Technology's "Go Open" Initiative homepage lists four compelling reasons to use OER:
1) Increase Equity - All students have access to high quality learning materials that have the most up-to-date and relevant content because openly licensed educational resources can be freely distributed to anyone.
2) Keep Content Relevant and High Quality - Traditional textbooks are perpetually outdated [...] The terms of use for openly licensed educational resources allows educators to maintain the quality and relevance of their materials through continuous updates.
3) Empower Teachers - Openly licensed educational resources empower teachers as creative professionals by giving them the ability to adapt and customize learning materials to meet the needs of their students without breaking copyright laws.
4) Save Money!