But I presume it refers to the Sun's rosette orbit periodically plowing through the galactic plane. Supposedlly, this could cause problems by the increased star density or presence of molecular cluds gravitationally perturbing the Oort Cloud and shaking loose showers of comets to bombard the inner solar system. Actually, we are curently embedded in the very center of the galactic disk right now, less than 50 parsecs from the geometric center of the plane's thickness, and it doesn't seem to be affecting us very much.

It takes the sun about 200 Myr to circle the galactic center, during which time it must penetrate the disk many times, it's orbit oscillating about the galactic equator. Since life arose on this planet, that's about 15 orbits, and perhaps many more passages through the disk. We seemed to have survived ok.

There are a lot of "galactic" constraints to life proposed by some astronomers, including moving metallic gradients in the Milky Way disk, the effect of multiple planets, binary and variable primaries, presence or absence of moons, and so on. Personally, I believe life is so robust, adaptable and ubiquitous, that I think any world where liquid water is possible and the sun varies by at most a few percent is likely to have life. It's a logical extension of the Mediocrity Principle (There Ain't Nothing Special About Us), which is one of the few things I accept on faith simply because so far it seems to be true wherever we look.