when you use AAS, they cause your natural test production to shut down. several processes in your body are dependant on testosterone, as are mood, vitality (a general feeling of lethargy is felt on low test levels), and most importantly...LIBIDO! some compounds shut your natural test production down so hard, erections can be next to impossible, and a general lack of interest in sex is felt. test does have it's share of side effects, but so do ANY AAS

aside from the above...test should always be included for muscle gain

test is should always be the foundation of any cycle. your can't build a house without a foundation.