When to use Variable classes? (BooleanVar, DoubleVar, IntVar, StringVar)

Can't tkinter.widget.configure(text="our text") be used for all widgets? What is the advantage, or the main purpose of using:

var_cls = tkinter.StringVar()
tkinter.widget.configure(textvariable=var_cls)

Is it that var_cls can be more easily shared among methods/classes etc?

Example with a Variable class:

import tkinter as tk
root = tk.Tk()
var = tk.StringVar(value="This will be on the label.")
tk.Label(root, textvariable=var).pack()
root.mainloop()

Example without a Variable class:

import tkinter as tk
root = tk.Tk()
tk.Label(root, text="This will be on the label.").pack()
root.mainloop()

In a tkinter application, StringVar (as well as IntVar, BooleanVar, and DoubleVar) are very rarely needed. The underlying tcl/tk interpreter provides special features for all of its variables, so these wrappers exist to take advantage of those features.

The two big advantages that these variables have are:

1. You can associate one variable with more than one widget, so that two or more widgets display exactly the same information all the time
2. You can bind functions to be called when the values change.

My opinion is that you should not use them unless you specifically need one of those two features. If you just need to get or set the value of a widget there are methods to do that on the widget itself (eg: entry_widget.insert(...), label_widget.configure(text='...'), etc).

I feel that they add overhead by introducing an additional object that needs to be managed, without providing any extra benefit unless you're taking advantage of the two features described above.

StringVar can be bound to a widget, so you just need to have a handle on the StringVar and you can modify its value and it will update automatically. Otherwise, you would need to keep a handle on the widget itself and handle the event loop stuff etc. Basically you should use StringVar etc. when the value could change. If it's going to be static for certain, you don't need it.