In my early 30's (I'm 42 now), I was at the tail end of losing 80 pounds before I was due for my annual bloodwork. My T levels were like 200ish. Doc asked if I wanted to be on it. I was lifting, gaining all my strength back from early 20's and thought "why the hell not". Really wasn't seeing any trouble with fatigue or other symptoms.
In the 3 months I was on it, gains galore in the weight room and I started getting tendonitis everywhere (shoulder, pec tendon, left hip, right lower quad tendon, forearms, etc) when I'd never experienced that before. When it got to the point that I could hardly work out my quads at all due to tendonitis in the massive tendon above my knee, I said "eff this" and got off.
I quit lifting again about 2 years later (because laziness) until April this year. I had my annual bloodwork done this year after I'd lost about 15 lbs already, and my T levels were about 250. First time since that I've been below 300. I know it's likely just the consistent caloric deficit and that I'm apparently one of men that doesn't experience too much of the negative effects of having a low normal T level.
I'm consistently being able to up weights on all my lifts even on the caloric deficit (layoff lifting newbie gains), and I don't experience a lot of the classic other low T symptoms.
Part of me considered going back on because it would only help my short-term fitness/physique goals, but the fear of never being able to come off and being honest with myself for the likely reasons for my low levels persuaded me against.