For me at least, travelling is not a big time-waster in the sense that I can be very productive too (believe it or not) while sitting at the airport lounge with my laptop, or while waiting to catch my next flight, or simply by "being out of the office", as long as there's WiFi connection back to the company's VPN/Mail Server.
Not sure about other colleagues in the industry, but quite a lot (and I do mean A LOT) of my time at the office is spent receiving and fielding telephone calls (even calls that don't have to concern directly to oneself, but since I'm there physically they pass it to me "because maybe I know and can solve"; mainly tech-support related calls with "newbies" questions from end-users) causing constant interruptions.
So, travelling can be seen as a "productive escape from the office" for purposes of reading & gathering information for a prospective customer or planning for a big project, review your numbers and margins on the Excel price list, doing research online and update your obsolete Powerpoint from 3 months ago, posting on IPVM : ) hehe..., etc. things that are sometimes difficult/impossible to do in the office with others constantly interrupting.
How can my boss be sure that I am productive while out travelling ?? .. I make sure to answer all his e-mails within 3 - 4 hours, the same day.