Is it necessary to send steady streams at 1hz or we can change to 2 or 3 or (any number)hz. If it can be, what will happen, what is the concept of sending stream at hertz.
I have just started using ROS and i am little bit confused by why we have used only 1hz.
Without a link or an example of "sending steady streams at 1Hz", it's a bit tough to understand what you are talking about. Guessing you were following the introductory tutorials I glanced at the Pub/Sub pages in Python and C++, and they both use 10 Hz loop rates. Perhaps it would be useful to update your question and provide some references that indicate why you are even asking this question. Who is we? Where are we only using 1 Hz?
I know of no limitations in anything related to ROS that strictly requires 1Hz rates.
I want to know the concept of using it.