You dont have to use the Object repository.

u can write scripts using the Scenarios,u dont have to wait 
for the application to come.

We no need to depend on OR.
we will write the property and values in the script 
statements it self. so that qtp will identify based on that 
properties. no need to depend on OR

ex: window("flightreservation")winedit("userid").set "siva"
with the above example it will go to identify the userid 
edit box using OR

and where as in Discriptive programming.

window("attachedtext:flightreservation")winedit
("attachedtext:userid",.......(no of values to 
identify).set"siva"

hai siva

window("attachedtext:=flightreservation")winedit
("attachedtext:=userid",.......(no of values to 
identify).set"siva"


this is correct script
if you want any dout 
make a call i will explain


9916398678

We can go for descriptive programming in the following
situations
1).When application under test (AUT) is not ready.But if we
the objects and their properties then we can prepare the script
2).If same type of objects present in multiple pages then it
is difficult to maintain object repository then also we can
go for descriptive programming