You probably notice when your friends and neighbors have had their yard aerated. They have little plugs of soil all aver the yard that are just laying there. Why do they aerate the lawn every year?
When you aerate your lawn it opens up the lawn to receive more nutrients, breaks up the thatch, and just plain lets the lawn breathe. The soil plugs will break down over time and are fine to leave on the ground. Seeding the lawn will help the lawn thicken up for the next season. The thicker and healthier your lawn the less weeds you will see.
If you are going to aerate and seed the lawn yourself this year make sure you rent or borrow an aerator that leaves plugs and you use a high quality fescue seed mixture.