Everything VLC needs to play media files is contained within which means no outside codecs are needed. This makes it one of the most hassle-free music players as it can play virtually anything as soon as it's installed.
Yes. Lightest. Even better than the ones known to be light. Both when playing music, only a single song or when playing a video. Either in terms of RAM or CPU. Compared with almost all, including the ones from Windows like mpc-hc, or light ones from Linux like Alsa Player, Audacious, SmPlayer.
VLC is an incredibly robust application but very simple on the surface. It makes playing music simple, yet still manages to give the user all the tools they want in a music player.
Browsing large libraries causes slow down and stutter, there are overlay issues when starting a video, and in general some video does lag especially when using lower end hardware.