Thanks for writing. Part of the answer depends on what look you like. Many types of holly can be pruned into tidy, specific shapes or left to grow naturally. Or have the tips of the branches pruned to allow the plant to grow in a natural form but stay smaller.
Nandina is often pruned just to keep the plant looking neat --- so removing old wayward stems or branches that don't look so good any more.
---Justin, Senior Garden Editor, BHG.com