Dijkgraaf - 12:12 am on Feb 9, 2012 (gmt 0)
If you have a table for each section, each time you want to add a section you have to create a new table.
If you have one table that contains the name and ID of all the sections in your forum and another that contains all the posts in the forum (and which section they are in), all you need to do (if you've coded for it already) is add another entry in your sections table to create a new section.
Also by having things in separate tables you aren't really spreading the load as you still will be doing about the same number of read and writes.
If have separate tables and you then also want to add search functionality across the sections, you would have to search through each table, rather than just one.