Trusts are often used for tax planning reasons, as well as to protect assets held for young people or vulnerable adults.
Trusts can also protect assets that are to be used to help someone who is in receipt of means-tested benefits, without affecting their right to those benefits.  They can also provide protection for someone who you would like to benefit from an asset, but who (for whatever reason) may not be able to deal with the management that asset for themselves.
Trusts are an important part of estate planning and are often included in wills, especially when second marriages/ civil partnerships or blended families are involved.