It doesn't necessarily has to be a bad decision, my grandmother did that to students for a number of years and it was a good way for her to increase her low income, so it depends a lot on the situation.
I wondered if this was just something that you would see in larger cities. I am in the suburbs down south and I have never encountered a lease that allowed for subletting, and I used to work for a rental agency. I think for the most part you are probably better off not allowing tenants to sublet. That way you still have some control over who you are renting to.
The issue with subletting is that sometimes it's not on paper, so it's a risk. We might risk getting caught, but if we do not get caught we can make good money with it.
First of all the sub letting should not be allowed as it is really cumbersome idea. U believe that tenants should start leaving in the house when they start paying the rent. Subletting should be strictly prohibited.
Your post doesn't make much sense shilpa, what's wrong with subletting? If you have the place and you have an extra space, it's a good idea to make some extra money, so hard to come by these days.