What use is the Tag property in Winforms?

I have noticed the Tag properties with controls. Is it okay to use this to reference my custom objects, or should I stay away from it as it would require boxing and unboxing which has been mentioned as unsafe and is not recommended.

TreeNode tn = new TreeNode();
CustClass o = new CustClass()
o.number = 123;
tn.Tag = o;

class CustClass
{
    public int number {get; set;}
}