Gh can be very BAD for somebody under 25. It can screw up their endocrine system as the system isn't fully developed yet until typically the mid 20s.
Gh won't make them grow bigger and stronger by itself (99% of the time). It will aid in fat loss. It will help connective tissue. the problem is, it can be so painful on the joints for some that it is completely debilitating.
Most folks do inject it into the fat on top of the abs. This is suppose to help with spot reduction of fat.
If your friend is not an older guy like myself, it is a pretty damn expensive way to go about dropping some fat. For us old farts, it helps our tired old joints, our skin, and we sleep better at night. For young guys, they don't typically notice this sort of thing.