There are a few reasons why I'm topdressing the lawn. Its quite bumpy
overall and uneven at places. There are certain areas where the grass
is pretty much dead (thanks to grubs - which I will tackle this year as
well). The current soil itself has a lot of clay, so it doesn't absorb
water well, and in the areas exposed to Summer sun all day long, it
tends to get rock hard and crack. I'm hoping the extra layer of
topsoil will help make it "softer" and give a better chance for grass
to grow. Finally, at certain areas (mostly near my house or a few feet
away from the hedges) I'm changing the grade, so for those areas I'm
going beyond simply topdressing and adding up to 8" of new soil (and
seeding completely as though it was a new lawn).

Last year I aerated the entire lawn, and the thatch isn't too
compacted. This year my main goal is to get a more even lawn (less
bumpy and better grade), and to get grass growing in areas where it
usually has trouble. I also want to get rid of the dandelions once and
for all (well, the majority anyways). It usually takes me 3 sessions
(weeknights or weekend afternoons) to remove all the dandelions once
they have grown (50' by 45' backyard). And they come back every year,
so that's why this year I'm going with the chemical route.