Roaming profiles and .oab files killing them

When using windows roaming profiles I find that .oab files are the source of many roaming profile errors. I find that these files for some reason are making the profile much larger than it actually is. In my current situation our File Servers accounts are defaulted at 700MB and the .oab files are a source of many profiles going over this limit. When deleted everything works properly, but if not deleted it wreaks havoc on our customers. I am wondering how the .oab file is created, why its created, what it does, and how I can stop them from being created? Anyone with any ideas???