Imitation is a very significant component of the learning process, not only as it applies to voice over delivery but in other artistic areas as well.
Writers learn to write by imitating other writers’ styles. Artists learn to paint by imitating other artists’ styles and brush techniques. Composers learn by imitating other composers.
The idea is not to turn your delivery into a clone of the style you’re imitating but enabling you to use some of that style and merge it with a portion of other styles learned by imitating other sources. Thus, the style of Hemingway, Picasso, or Stravinsky is formed by a combination of the styles they have learned by imitating their accomplished peers, and they have made conscious or unconscious choices as to how little or how much of each source to incorporate into their own creative mixes. The voice over student learns in the same way. Avail yourself of every opportunity to seriously analyze and imitate people whose styles you admire. You will discover that many of these styles will not be a good fit for you, but several will be. You will discover in time how much of each you want to retain to create your own combination, hence, your own style.