if its for a full body workout, have 4 different workouts that you can interchange... it stops boredom as well as stagnation in terms of mucle growth/devlopment.

a muscle has to have progressive stresses placed upon it to force it to adapt... tapping it with light weights will only get you so far before you heavily plateau.

depends on your goals, sport orientated muscle training or bodybuilding.

i am a martial artist so i cater my workouts like wise to allow explosive movements as martial arts sparring matches are one 3 minute round, hardly a 12 round marathon so i need strong fast twitch muscle fibres.