The value of Big-O notation is for scale ability and the value of the constant of proportionality!

[Casey Hawthorne]

The value of Big-O notation is for scale ability, since quite often a
an algorithm used for small N is forgotten about in a large program
and not changed when the program has to deal with larger inputs.

It's also useful to know the constant of proportionality, for
different platforms, for code optimization issues.
--
Regards,
Casey