Let’s face it. Collaboration is the backbone for most any process intended to move projects through stakeholder channels, final drafts and completions.
For collaboration security, it's not surprising that certain team members will often be assigned different levels of tasks requiring access throughout SharePoint’s document management modules. But, not everyone is expected to have the same privileges, for example, to add or edit content.
As such, Office Web Apps used in conjunction with SharePoint 2013 can provide useful tools with updated versions of Excel Web App, OneNote and Word Web App, for example.
Assigning permissions can key on the necessity for certain users to then edit Office docs in the Libraries; this, via a web browser.
Such access complements the editing and viewing on the array of digital devices today, from PCs and Macs to tablets/slates and smartphones.
At its core, the Office Web apps are accessed via its own Office Web App server---physical or virtual. Once SharePoint is configured to use the Office Web app site, then users can start access the tools.
Generally, there are two options for licensing the Apps: view only, which is free, and Edit/View. The latter choice requires the purchase of an editing license.
Excel Web (EW) app versus Excel Services (ES)---SharePoint
The two have similar features with ES offered only in SharePoint’s Enterprise suite. EW is available both in SharePoint server 2013 as well as Foundation 2013.
Excel Services allows users to integrate external data as well as to interact with elements like Pivot Charts, PivotTable reports and timelines. In short, it will provide more BI than the Excel Web app, but users won't be able to create/edit worksheets in a browser.