Microsoft Office Web Apps is the online companion to Office Word, Excel, PowerPoint and OneNote applications that enables users to access documents from anywhere. Users can view, share, and work on documents with other users online across personal computers, mobile telephones, and the Web. Office Web Apps is available to users through Windows Live and to business customers with Microsoft Office 2010 volume licensing and document management solutions that are based on Microsoft SharePoint 2010 Products. You could find the installation with architecture design.
This feature is very helpful if you have SharePoint users accessing Microsoft office documents from UNIX and Linus systems without Microsoft Office client installed.
There is a big risk if you plan to install this to SharePoint 2010. Our experience was that if an installation of Office Web Apps had to be uninstalled, the result would be that the server would be removed from the farm. We experienced this with several environments in November 2010 and notified Microsoft. Microsoft Product team confirmed on April 14, 2011 that the results we experienced are, by design, the correct behavior. The explanation is that the Office Web Application service must be installed on all web servers and must stay in synch across those servers. Therefore, to avoid a situation where the servers are not synched, the uninstall process removes the server from the farm.
Microsoft mentioned this will not be resolved in the near term and may not in next SharePoint version (2015?). Microsoft offered a couple of work-arounds. Microsoft will send us a white-paper detailing those work-arounds. One of the work around is to disable Office Web Apps if installation failed. However, the high risk is three is no clear procedure Office Web Apps could be upgraded to future version whence this issue been fixed.
The bottom line is that we consider the uninstall process and the work-arounds to be unacceptable risks to our environments and does not plan to use Office Web Apps in our SharePoint environments until an alternative low-risk uninstall process is provided by Microsoft.