Since 2 years ago, I started adding some T to see what (if any) positive effects it might have as I've been struggling for years with low energy/interest in life. I'm post-op since 2005 and I have been on estrogen alone or with progesterone, at low, medium and high doses.
I started with gel (Androgel) and recently switched to injections (T. Cypionate) which I prefer for its effects. I will admit that, despite taking some T, I still somewhat struggle with low energy/interest although at least now, there are days, here and there, where I feel an improvement but it's not constant. Mood is also overall, slightly better but still not where I'd like it to be. My skin has significantly improved since T. It's never dry, very moist and has some bounce to it. It shines. My vagina is also rarely dry these days, is so tender/elastic, lubricates plenty. My libido has significantly increased and I like it! I can now reach orgasms just with my clitoris and touching my nipples has become somewhat arousing. I also ejaculate a good amount. My memory (finding/retrieving words) has also gotten better. And my cellulite....OMG, has MAJORLY improved, none on my thighs, much much less on my buttocks. I lost some weight too and my body looks better. Hair gets oily faster so I need to wash every 3-4 days instead of weekly. No other side-effects.

p.s.: since switching over to a new compounding pharmacy for my estradiol valerate IM injections, a few weeks ago, I have surprisingly noticed further improvements in my skin, hair (thicker, fuller, softer) and my interest in life as well as energy have improved somewhat significantly. My appetite has also increased. I take a HIGH dose of estradiol and inject frequently. I also supplement with Estrogel, all under the supervision of a doctor who is well versed in the matter and gives me freedom to try.
I don't aim for a level but instead titrate dose according to physical/psychological symptoms. Every individual is different and intracellular concentrations cannot be had with blood tests.