To check undue proliferation of special economic zones (SEZs), approval given to such enclaves should be cancelled if they do not start functioning within a timeframe, a key finance ministry official said. "SEZs are essentially a good thing. Because they are helping us in inflow of investments and generating employment. But you should not have SEZs just for the sake of SEZs,' HAC Prasad, senior economic adviser in the finance ministry, said. Prasad was a key member of the team, which penned External Sector Chapter of the Economic Survey 2007-08. The survey has called for checking the proliferation of SEZs. "What we said is that there should not be undue proliferation of SEZs. There should be some timeliness within which these SEZs start functioning and yielding high exports,' he said. These zones should yield high exports within that timelines, so that economic activity is expanded and employment generated, Prasad said. "But, if SEZs are sanctioned, I think it has to be seen that they take off. It they are not taking off, then after some time possibly we have to cancel the sanction given. There is no question of sitting over SEZs and saying I have got SEZ and not implement it,' he said. He, however, said he did not have any number in mind which could be considered optimum for SEZs in Indian context. "I don't want to specify a particular number. We have to keep a constant watch and monitor them, and at the sanction stage itself, we have to see that they are potentially good SEZs, and not have too many SEZs at the same place,' Prasad said.