This covers a whole range on things from 'bondage' to 'torture' it is there to clearly inform the slave of his position in life and the power that you have over him.

When the slaves has ball weights on stretching his worthless sore nutts only to the coldness or the edge of a blade as Masters circles the slaves tight ball sack, the sharpness of the blade dragging across the skin, as the Master tells you what a worthless piece of shit you are he pulls away the blade and a trickle of blood drips from the glint of the blade...

This is always a nice little reminder for the slave demonstrate the contrast between Master and slave,  as you move from symbolic emasculation to the actuality of having your slaves balls cut off!

One slave I knew of had the ball weights on for months as a constant reminder of the Master that put them there, a similar effect can be had with a cock cuff.

Sensitivity ^

Not all slaves are the same! You need to give some consideration to the slave that you are playing with, some have balls so sensitive that you can hardly touch them. Like if another slaved licked them too hard he night have problems. Other slaves can take a lot more stimulation and again each have different recover times.

You have to give some consideration as to how your slave is 'wired' inside.

You need to understand just how far you can go, what the limits are. The slave wants it heavy, but what does heavy mean to him. My boyfriend would have a problem with anyone but himself touching them, where as a number of my slaves can take their balls being spanked. Also remember that a slaves limits can vary dependant on mood, sometimes he can take more other times less.  This is one benefit of having a regular Master that knows the slave, so knows what 'heavy' or 'light' equate to, a stranger is not so well informed, and can either be dull (under performs) or a "dangerous top" because he over performed for you. This is why there are all sorts of Masters for all sorts of slaves and it takes time to get the match right for you.

Inspections ^

It is also the Masters responsibility to inspect the slaves balls to ensure they are healthy and there is no reason to have a doctor inspect them. This can be incorporated into the general handling of the slaves balls, feeling these little beads slipping inside the ball sack as you grip them. Remember that Cancer of the balls is as common as breast cancer in women, but is easy to cure if found in time.
If you find any hard lumps down there get him to Doctor for a check-up, this sort of Cancer is very easy to treat and the cure rate is in the high 90%. It is very unlikely that a slave will inspect himself (fearing the worst) this is why the Master has to take control.