The berries give a gentle flavour of allspice and should be removed before serving a meal, but using the powdered version will give the same effect - careful with the amounts - taste when adding it so you do not overpower the meal.
Allspice oil is also avilable- its useful in treating tooth pain, a bit like oil of cloves, but it can cause nausea if swallowed.
Health food shops should have the whole berries if you want to use these - you can of course grind them at home, or roasting them before using will enhance the flavour, as nearly all of the spices used carry thier flavours in oils in the original plants, and gentle roasting / heating releases more of the oils.