When to use numeric or string handles

Hello MATLAB/Simulink programmers,

I wonder when to use numeric handles and when to use string handles to Simulink blocks during programming MATLAB scripts/functions. I've been using numeric handles all the time, but actually I don't know why. I see one main disadvantage of numeric handles: they are not valid any more when the model is closed and reloaded. This might be annoying when debugging.

Are there any more advantages/disadvantages? Which kind of handles do you use? And when? And why? Are there any recommendations by MathWorks?

Many thanks in advance Thomas