Sorry for creating a new thread to ask such simple question, but I can't find the answer anywhere. When do I need to declare this kind of section?

Primarily only in DLLs, but in general for any executable which might need to be relocated. If the base address (defaults to $400000 for executables) conflict with other loaded resources then windows will attempt to relocate to another base when relocation segment is present. Also, there is a security feature (only in Win7?) to locate programs at a random base - iirc, it also requires a relocation section to work dynamically.

Afaik ASLR was introduced on Vista (although it might have begun in a pre-vista server edition of Windows) - there were some changes for Win7, but I can't remember the details and don't have an URL handy, sorry. To enable ASLR for your executables, I believe you need both the .reloc section as well as some header stuff, here's a short description.