I'm currently finishing an anabolic cycle with low dose T3. To be honest, I got mostly sides and not much extra anabolism. By sides, I mean lethargy, in and out of the gym, less endurance on lifts, etc., higher heart rate, and night sweats/**** sleep. My lifts have gone up though...but not more than they would with 30mg. of E...Max and 1T/4AD/4OHT trans on its own.
I never went over 25mcg., and I also added T2 in low doses (100-200mcg) to potentiate the T3 (as explained in many studies).
I do notice that if I take T3 on an empty stomach (as recommended in the Cytomel lit), and don't eat within an hour, I have a major hypoglycemic problem.
The theory is this: thyroid hormone speeds up the rate at which nutrients are metabolized. Your trusty AAS maximizes nutrient partitioning to create a favorable environment for growth. Put the two together for faster gains.
Personally, I'd rather use a different approach--better AAS, different stack, non-hormonal solution, etc.