In a recent project we wanted to migrate a SharePoint 2010 sitecollection to 2013. But there was one site, that was huge. Even though we migrated it over night, the next day the migration process still was working. A deeper look into it showed, that all the huge lists had been migrated. But we didn’t think about the workflow history list. It had about 100000 items in it, first one created about 3 years ago. There where a lot of workflows on this site and every workflow wrote into this list.
So, for now on, every workflow I create has an own task and history list and I will use the information management policy.
For further and deeper information, read this very good article by Marj Palmer.