There will usually be a period after buying the property where, if you sell the property, you will have to pay back all or part of the discount. Ask your council for more information if you are likely to sell the property within a short period of buying it.
Many tenants have seen that this is a good way to buy their first home either to live in permanently with the security that they will never be required to leave the property or to have as a long-term investment as the first step on the property ladder.