The session/process logs has very useful information for troubleshooting, but as corey mentions the table can grow super quickly (the audit log table does too). You can set the BP environment to archive the logs older than a certain time frame (1 week, 1 month, etc). Take a look in the System tab > System group > Archiving. If you've never done this before, it'd be a good idea to use manual mode to archive pieces of it first rather than doing it all at once.
Dave Morris, 3Ci at Southern Company