The Helvetica is essentially a neutral font and therefore it is particularly used in signage. On the other hand the Helvetica Bold is used when something needs to be highlighted in a text. The Helvetica Bold Oblique on the other hand is a font that has much more character than the original Helvetica.
It is therefore widely used by graphic designers and advertising agencies all over the world. This font can be creatively used as an ornament on an otherwise simple document. With this font a piece of text like a party invitation will require no other ornamentation to make it look special.
See also: Free Helvetica Font: Helvetica Bold