Boosts are used to BOOST trades...as you can see in OUT SETTINGS you can define % of total out traffic which will go to BOOST TRADE. By default trade where you assign high boost will get 15% of total out traffic and NITRO boost will get 30% of total out traffic.
BOOSTS are used when U wanna PUSH STRONGLY tarde or U can use for example NITRO BOOST to grow trade which is MUCH BIGGER then your site(in traffic).