1. Some IMEs have special reading characters. For example, an IME may use bo po mo fo as its reading characters, and another IME may use some radials as its reading characters. An IME can provide a soft keyboard to show these special reading characters so the user won't need to remember the reading character for each key.
2. IME needs to change the reading characters of keys according to different conversion states. Using a soft keyboard can notify the user of the change of keys. At candidate selection time, an IME can show only those selection keys to user.