It means when you break a spoke in back, it'll more likely be on the non-drive-side than the drive side.

Lacing the non-drive side with cross lacing (required in a rear wheel to transmit the drive torque to the rim) allows more balanced tensions between the drive side and non-drive side spokes than a more traditional construction (cross both sides, or crossed on the drive side and radial on the non-drive side). I don't think there are any weight-specific advantages to the construction, and I doubt you'd be able to tell whether you're riding an Isopulse wheel if you were doing a blind A/B test.

Isopulse lacing does force the torque to be transmitted through the entire hub body and onto the non-drive side flange instead of putting all the strain on the drive side flange of the hub. If the hub is engineered for it (and it should be) this also shouldn't be anything you notice.