I replied in another topic with this question. However I wanted to ask here as well. I remeber reading somewhere that you should remove the expander ball when neck or partial re-sizing brass. Is there any danger here?

Some people do it but they would be a minority. Most people do it because they are getting bad runnout when they pull the brass over the expander ball. If you have a runnout gauge I'd see if you are having a problem with bad runnout using the expander. Otherwise leave it in there. If it wasn't an important part of the die the manufactuer of the die would leave it out or would tell you to experiment with it out.
You certainly can experiment with taking it out. I would then check and see how far under caliber your case mouth is. To me it should be no more than .004-.003 under or when you use your bullet as the "new expander ball" it will be hard to maintain straight seating under the extra effort it will take to seat the bullet.
Some people neck turn brass then leave the expander out...after taking some off the neck the die won't over work it and you might be back to near tolerance. Some people leave it out of the die then plunge the brass over an expander ball from the mouth of the case down into the brass...that does seem to leave excellent runnout but is an extra step.
I would recomend that you get a runnout gauge and if you have bad runnout fiddle with the expander stem until you get it centered in your die and it is making great runnout. Many time just giving small turns of the seating stem in one direction or the other will center the ball and runnout will be near perfect.
Well,,,,enough rambling and idea throwing.
If you have a fav cartridge I highly recomend you get a lee collet neck sizer....all your runnout prep problems will be over....Midway has them on sale in their latest flyer for about $17.

I never used an expander ball when I used "S" bushings. It's not needed if you use BT bullets. I only used .002" neck tension on "normal" cartridges and .004" on magnums.

I pulled the expander from my S bushing dies and put it on my FL (which I never use) in case I wanted to expand only the mouth of the case for non BTs, but never really did that either.

I've recently converted to Lee colett neck dies, which I really like better'n the S dies.

You need to use the expander with standard sizing dies. Most all dies sized down the neck area much more than needed.The expander opens the neck to the correct inside diameter. The brass might be damaged if seating a flat base bullet. Boattails are more forgiving and act like an expander on seating.

I use LEE Collet neck sizing die.

I lube the inside of neck, makes neck sizing more accurate.

Unless you neck turn brass for a custom chamber you should always use the sizing button (expander ball). When you size either FL or neck or partial neck you push all imperfections to the inside of the case. The sizing button pushes the imperfections back to the outside of the neck so no interference seating the bullet.

Always inside neck lube.