[<< wikibooks] Open Education Handbook/Benefits of open education
There are many organisations, groups and individuals who can potentially benefit from open education and open educational practices.
The OER Research Hub project investigates some of the key claims made about the benefits of OER and open education. Their research hypotheses provides a good overview of the potential benefits.

Use of OER leads to improvement in student performance and satisfaction
People use OER differently from other online materials
OER widen participation in education
Use of OER is an effective method for improving retention for at-risk students
Use of OER leads to critical reflection by educators, with evidence of improvement in their practice
OER adoption brings financial benefits for students/institutions
Informal learners use a variety of (quality) indicators when selecting OER
Informal learners develop their own forms of study support
Open education acts as a bridge to formal education
OER use encourages institutions to change their policies
Informal assessments motivate learners using OERThe latest evidence for these claims can be reviewed at OER Impact Map. 
Much has been written about more specific instances where open education approaches can bring benefit. 
The Commonwealth of Learning report Benefits and Challenges of OER for Higher Education Institutions notess that: "anecdotal evidence suggests that OER may improve educational practices, coherence across courses, technical quality and research into pedagogy; facilitate technical improvements and the development of high quality and shareable images; and improve mechanisms for accreditation and external endorsement. Survey responses suggest that OER does not reduce materials development costs directly, but instead is still requiring additional funding. However, OER may indirectly increase the number of registrations thereby increase tuition fees; lower some of the marketing costs; and enable a new business model through offering services around OER."
Institutions have also benefited from open data and transparency that can lead to better funding and infrastructure.  
The Open Michigan report Open Educational Resources: Benefits for Faculty and Students argues that openly-licensed learning materials are easy to find and access, encouraging more independent and flexible learning opportunities for students. OER courses allow students to explore materials before enrolling, making them better prepared before they arrive in the classroom. 
Open education has given access to those who previously had no access to educational materials, resources and practices. This means that someone can study using a Massively Open Online Course (MOOC) or OER generally without having to attend a formal learning institution.

=== Further resources ===
Benefits of openness in education - wiki for Open Education Summit 2012