In fact one can lose the money as investment in equity can be risky as well. The person willing to take some amount of risk can use this combination. However, with an over limit of Rs 10,000 that's the maximum risk with your tax saving investments that you can take. You can invest beyond that as well, however, the tax rebate would be available only on Rs 10,000. But then if ELSS are more risky why should one invest in them.
High risk means the probability of high return.
There is a compelling case for PPF when one is looking at a assured, safe, tax saving option. Rs 60,000 worth of investment in PPF as one gets with the infrastructure bonds, but the interest income in case of PPF is absolutely tax-free. The person who is not willing to take any risk and wants assured return can use this combination. However, one an take a loan or withdraw partially at the end of 7th and 3rd year respectively. With Bonds while the interest is taxable, the lock-in is much less.