This question comes up when talking about the OCS hosted Live Meetings when customers are trying to decide how much space to allocate to the Web Conferencing shares.
There is an article on TechNet that talks about the recommended space to allocate per meeting, the maximum size of documents per meeting, as well as how to modify the size limits. I have included the table below:
PowerPoint Documents, Word Documents, Multimedia, or Snapshot Slides
The size of a file must not exceed this value.
The total size of all files in a conference must not exceed this value.
Number of files
The total number of files in a conference must not exceed this value.
You can read the whole article here: http://technet.microsoft.com/en-us/library/dd572518(office.13).aspx