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If there are likely to be millions of some type of object,
then avoiding gc for that type on grounds of reducing memory
use may be arguable (or, as in the cases of tuples or lists,
may not be arguable regardless).  Else "if it points to a
PyObject, it might be in a cycle, so gc-enable it" generally
rules.

I'll note in passing that the m235 and fib generators
weren't _intended_ to stress Python in any way, but have
been extremely effective at doing so since generators first
went in.  Think of them as a pair of canaries in the coal
mine :-)