Step-by-step explanation:
advantages - more effective and therefore a higher chance of success. since a genome is usually produced prior to procedure, risks and allergic reactions can be reduced effectively. little to no side effects are noticed as a genome analysis is done before. often the problem can be solved from the root in gene therapy.
disadvantages - ethical issues as often people are not comfortable in genome analysis. can be too expensive as gene therapy requires advanced technology. in the case of using radioactive elements, it may lead to mutations that may be a bigger issue than the disease itself.
hope it helps. :)