1. Taking the risk that the recipient may not be able to access the data

1. A proprietary format makes the use of a specific software compelling for having access to the file content. By exchanging files in proprietary formats you tacitly assume that all the recipients of your file possess the software needed for opening the file: any user that for technical reasons (e.g., users working on a different platform) or financial reasons (users that cannot afford buying the required software) cannot run that specific software, will never be able to use the file.
2. Now, let us assume the user possesses the application needed to open the file. Will this guarantee the complete accessibility of the file content? Unfortunately not: a strategy largely adopted by software producers consists in regularly upgrading the data formats they implement in their applications. Such strategy is meant to lock the user in to the use of a specific proprietary software. In this way, the only way for the user to assure future accessibility to his/her own data or to guarantee perennity to old files is to regularly buy updates of a specific software.
3. [Semi-proprietary formats and predatory and predatory practices]. A similar strategy to lock the user in to a specific data format (« Embrace and Extend »∞) consists in adopting at the beginning an open format for storing a software data and then progressively modifying this format with proprietary extensions, which make the resulting format incompatible or unreadable with other software based on the original format. This strategy are often adopted to turn a public standard in a semi-proprietary format.

The adoption of proprietary or semi-proprietary formats is the result of corporate strategies that go against the user's needs, which should privilege accessibility, interoperability and perennity of exchanged data.