New Install vs. Migrating

A fresh install would mean:

1. No database so no group structure, nor group polices and no historical data about threats or computer history (the last one can be important to companies tracking year-on-year threats).
2. The server would create brand new certificates and all existing endpoint installations would then have out of date certificates.  No real problem if you plan to re-protect all the computers.  However that is a consideration about losing the old certificates:
3. Assuming you kept the same server hostname/IP address for the server the clients, with the now incorrect certificates, would be able to route messages to the new server but all those messages would be blocked as the certificates won't match.

If you don't need the computers, groups, and historical data in the database starting fresh on that is simpler and forgoing the backup/restore will save you some time.  However it's always worth copying over the certificates...

http://www.sophos.com/en-us/support/knowledgebase/117463.aspx

...especially if the new server has the same network settings as the old one as you avoid 55 computers trying to send messages to the Sophos Certification service and that service having to repeatedly deny the request (which slows down valid messages trying to get processed in the queue).  You would generally have to have tens of thousands of endpoints to really see a problem but I have been involved in troubleshooting that so I now suggest thecertificates are always kept.

A fresh install would mean:

1. No database so no group structure, nor group polices and no historical data about threats or computer history (the last one can be important to companies tracking year-on-year threats).
2. The server would create brand new certificates and all existing endpoint installations would then have out of date certificates.  No real problem if you plan to re-protect all the computers.  However that is a consideration about losing the old certificates:
3. Assuming you kept the same server hostname/IP address for the server the clients, with the now incorrect certificates, would be able to route messages to the new server but all those messages would be blocked as the certificates won't match.

If you don't need the computers, groups, and historical data in the database starting fresh on that is simpler and forgoing the backup/restore will save you some time.  However it's always worth copying over the certificates...

http://www.sophos.com/en-us/support/knowledgebase/117463.aspx

...especially if the new server has the same network settings as the old one as you avoid 55 computers trying to send messages to the Sophos Certification service and that service having to repeatedly deny the request (which slows down valid messages trying to get processed in the queue).  You would generally have to have tens of thousands of endpoints to really see a problem but I have been involved in troubleshooting that so I now suggest thecertificates are always kept.