Some might say you wouldn’t need a dedicated web hosting company to do your standard forum hosting, and they might be right.  Under some circumstances and depending on the scripts you are using to make your digital world go around, dedicated hosting might not be a bad way to go. 

Web sites that are overly popular could probably do with the power and performance a dedicated machine could deliver.  Look at limits like disk space and bandwidth, sure.   Don’t forget though about things such as CPU power and RAM.  The more of that you have the smoother your forums will run.

Some server side scripts to run your forums or message boards can be demanding too.  One of the most demanding is vBulletin.  Now you might be able to get away with running it on a shared machine but you would be much better off on a dedicated one.  I can be a big server hog at times, so be sure to feed your hog with the server resources it needs to survive.