From the Montreal Gazette:
Tim Weis, the director of renewable energy and efficiency policies at the Pembina Institute, an Alberta-based environmental research group, said public transit agencies that want to plan new services, routes or incentives for commuters, also benefit from answers to questions on the long-form census that ask people how they get to work.
"When you're looking at programs for energy efficiency or programs for public transportation, some of the things you need to know are the sizes of houses, how they're living in them and how they're getting to work," said Weis.
It is fairly straightforward to see how this would happen, at least if we assume that people won't fill out a voluntary census as eagerly as they would a mandatory census. The city of Ottawa, for instance, is targeting a 30% modal share in public transit users, a statistic readily available in the federal census. Establishing benchmarks for transit policies as well as measuring the city's progress against those benchmarks will, in all likelihood, suffer is the mandatory census is made voluntary.