Why does Python allow stand-alone expressions?
The python creators decided that any expression is valid as a statement. While not all expressions are useful as statements, it would make the language more complex to have to remember which expressions may be statements and which can not.
A second reason is that many expressions that may seem &quot;safe&quot; can still have side effects, making it useful to evaluate them without using the return value.
Operators
Operators are the most obvious examples of expressions that you can easily add side-effects to. In your example 0 &lt; 0 is equivalent to 0.__le__(0). You can overwrite the __le__ method or any operator special method to do whatever you want, including writing to a file or incrementing a counter.
You can also evaluate operator expressions just to make sure the types are compatible. For example, if you are going to do a very long computation on variables a and b that ends by dividing some value based on a by b you might evaluate a/b at the start of your function as a quick and dirty way to make sure the types can be divided and that b is not zero before spending a lot of time calculating.
Strings
Strings don't typically have any side effects, but string expressions are frequently used in python code as a type of comment. Specifically, docstrings are triple-quoted strings right after the heading of a class or function, and will be assigned to __doc__.
Variables
Evaluating variables has one important function: It will crash if the variable doesn't exit. For example, suppose I have a module server.py that must be configured server.host = 'localhost' before starting. I could write this:
try:
    host
except NameError:
    raise ConfigurationException(&quot;must set host&quot;)

Tuples
The tuple expression a, b where a and b are expressions will evaluate any side effects from a  b.
Others
Ok, there is little use for a loose None. However, only disallowing None, True, False, Ellipsis, NotImplemented, and ... would be a unnecessary special case that would make the language harder to learn for little benefit.