This is great and very important, but it doesn't prevent burnout necessarily. I have a job and career that I really enjoy and consider to be very meaningful (aging research), but I have been severely burned out several times.
In some perverse ways, having a "meaningful" job can increase stress and propensity to burnout exactly because you know it's important. I imagine this is why doctors and lawyers have a lot of burnout, stress, and substance abuse problems. OTOH, you don't really hear about corporate accountants getting burned out.
My personal theory of burnout is that it happens when you start to feel you are on a treadmill -- running hard to achieve an important goal, but getting nowhere. Then the stress and burnout symptoms increasingly make this a self-fulfilling prophecy and feedback loop.