Being practical, you only *need* to attend a meeting if there is an
intractable problem in front of a WG you're actively participating in,
and solving that problem requires a face-to-face session.
essentially all of the work done at meetings happens in the hallways,
restaurants, and bars - when small groups of people get together to
work out mutual understandings and compromises which then emerge
as proposals to WGs. sometimes this can be done in email or over
the phone, but it's much easier in person.