Scientific research as long as there is enough space for the animals/plants to live comfortably and with a few members of their own species.
Natural Selection had them extinct for a reason. I'd only support bringing a few back for research purposes. And they shouldn't be released into the wild.
There are some species which went extinct recently and could be reintroduced.
If it's a species that humans caused to go extinct unnaturally due to pollution or poaching or what have you, then, yes, revive the species and release it into the wild. If it's not one of those species, then use them for research purposes and/or zoos only, but do not release them into the wild. Natural selection killed them off for a reason.
There are so many reasons why de-extinction is a bad idea than it is beneficial; we are playing God, we cannot control nature, it would devastate existing ecosystems.