They allow you to view the raw contents of files without trying to interpret said contents, which is necessary if you want to examine a file but don't have a specific program designed to manipulate that file type. I'm partial to WinHex, but there are hundreds of different hex editors each with their own features.
If you want to decode ADX to WAV, you need an ADX decoder.
If the game has the CRI logo somewhere in it, then it has ADX audio. MPEG Sofdec (*.sfd) is just MPEG-1 video with ADX audio in place of the usual MP3 audio that a *.mpg file would usually have. ADX is common for BGM, but I haven't seen it used for sound effects.
If you want to decode ADX to WAV, you need an ADX decoder.
If the game has the CRI logo somewhere in it, then it has ADX audio. MPEG Sofdec (*.sfd) is just MPEG-1 video with ADX audio in place of the usual MP3 audio that a *.mpg file would usually have. ADX is common for BGM, but I haven't seen it used for sound effects.