For example, some people choose an irrevocable trust when they have a large estate that could be subject to estate taxes. Because you're relinquishing ownership of irrevocable trust assets, you can use an irrevocable trust to reduce the size of your taxable estate. A revocable trust, on the other hand, won't lower your estate tax liability. Most people don't need to worry about federal estate taxes, though.
An irrevocable trust can also be used for creditor protection. Since the grantor no longer controls or owns the assets, they're generally off-limits to creditors unless a judge finds that an irrevocable trust was set up specifically to protect assets from pending legal action.
Note that revocable trusts become irrevocable trusts upon the death of the grantor, meaning that the terms can't be changed once the grantor dies.