""Doing things w/out a reason is folly. "" That statement - is not even close to being true!??!!? Do you think that's a reality - or - do you feel that's a reality? Anyways: Aerating for compaction is a legitimate reason, so for that purpose would it matter when the aeration is done? In areas where the ground freezes solid for the winter we have little problem with compaction in the spring. The spring thaw does an amazing job opening pores in our clay soils. If treated correctly, compaction can be minimal into summer. The lawns that are overwatered of course will start to compact with the first mowing.