Building science tells us there are 4 main elements to control
(listed in order of priority)
1. Water (nobody likes a leak)
2. Air (keep conditioned air in, unconditioned air out)
3. Vapor (keep it from condensing in walls)
4. Thermal (keeping the temperature comfortable.
The link below explains this in greater detail.
Save on heating and cooling costs
Improve indoor air quality
Prevent moisture & mold
Up to 40% reduction in outside noise
Defend against insects & pests