Do I need a trust?

Do I need a trust?
Hi-I have legal will in existence along with a living will re medical decisions etc. I have named a niece as executor. Despite this, relatives of mine are insisting it will be to everyone’s benefit to draw up a trust. They tell me this will avoid my property getting hung up after I pass. I’m confused as to why, since I have a legal, binding will, that a trust is necessary. Or maybe I just don’t fully understand what a trust is. Help.
Thanks
Donna