What is your system configuration, and how long have you been running OneWorld? We have been on OneWorld for over 3 years, and now have around 500,000 rows in our F42199 table; however, we're fairly low volume in the SO area. One program we found that updated this table quite heavily is that of SO Cost Update (R42950). We ended up changing the processing options and data selection to prevent this program from updating records unnecessarily, based on how our SO's behave. Also, you may want to see if the table is being hit by someone running a version of Item Master (P4101) with a processing option set to update 2nd & 3rd item numbers.
We've never purged our F42199 table, since it isn't used in any planning programs (e.g. MRP, CRP, Cost Rollup, Leadtime Rollup).