[tex-k] TeXbook: space -> control space

[Igor Liferenko]

Hi all,

It is still not clear to me from the TeXbook why it is "usually wise".
(i.e., is there any counter-example to "usually" and an example when
it can be "unwise")

Also, I would like to understand why a "tie" is not used in the
following line from the same paragraph:

    other common abbreviations like `Fig.'\ and `cf.'\ and `vs.'\ and `resp.';

Regards,
Igor