When do i need assign property and when not ?

Question

Can any one give me example when do i need assign property only...??

Answer 1

Every time you do not want to retain it.

Answer 2

1. Primitives: int, float, structs, etc.
2. Pointers to "non-objects": c arrays, functions.
3. Helper properties that you intend to retain in other controller objects. Delegates and handlers are common throughout.

Otherwise, refer to the memory management docs here. Pay special attention to the section on retain cycles.
http://developer.apple.com/iphone/library/iPad/index.html#documentation/Cocoa/Conceptual/MemoryMgmt/Articles/mmObjectOwnership.html