Well, I could try and explain this, but Microsoft did a pretty good job, so here's their definition of the patch:

The Microsoft Outlook and Microsoft Exchange clients each use a slightly different forms technology. When a user installs Microsoft Office 97 or Microsoft Outlook, their system is configured to run Outlook. So, switching to use the Exchange client can cause slower performance. Microsoft recognizes that there are some users who will use both clients on the same system (why, we don't know). To address these users' requirements as quickly as possible, the Outlook team at Microsoft has announced the beta release of the "E-mail Forms Fix Utility."