Just getting started? You can delay getting one of these. Frankly, unless you have the need for one, you could make a load of stuff never having one of these. But, if you are getting seriously into guilloché, you will probably need to get one.
A Leveling Chuck is used allow the turner to adjust how an object is being held. It allows for adjustments in the X, Y, and Z axes. This is especially useful for guilloché work and when turning large items where runout will become more evident and pronounced.
Disclaimer : eMail comments to me at OTBookOfKnowledge @ Gmail.com. The process of woodturning involves the use of tools, machinery and materials which could cause injury or be a health hazard unless proper precautions are taken, including the wearing of appropriate protective equipment.