for me, many things
-a lot more money
-better eating, sleeping, and lifestyle changes
-mental clarity
-no more paranoia
-better relationships with family and old friends
-getting back into old hobbies that I used to love before the drugs, and still do to this day
-a noticeable increase in maturity over many people my age
best of all, I find that I now spend no time trying to find any ways to get high all the time, and instead, use that time to devote to bettering myself, fulfilling my lifelong dreams, and getting involved in my passions and joys in life. I now feel like a normal person again, and feel like life has its meaning once again.
being a cokehead, etard, and a heavy psychedelic user for over a year, its been about 6-7 months off of everything (aside from one night where I did 2 lines of coke during SXSW really drunk). the road to this point has been filled with depression, anxiety, a feeling of emptiness and what not, but it has been more than worth it. if i didn't stop, i probably would have ended up dead within a few years or even months.
EDIT: I still drink and smoke weed occasionally, and have taken prescription meds (only when prescribed of course) during this time.