I’m going to add to my view. I think the only time I would willingly do this, is if I was getting taken out by an enemy that held a significant lead. If throwing all of my ships into my enemy and transferring control of my remaining stars to my ally, I could even their relative strength up, then I would consider doing it. Though, in that case, I would also keep one star, as far into my ally’s territory as possible, then share my income and any tech could acquire.
Also, thinking back, I did benefit once from this kind of move. It was a dark game with fixed scanning. I could only go one direction. My enemy and I had been transferring 2 stars back and forth for about 2 weeks. He started getting hit from the other side and figured it was over. As a parting gesture to honor the hard fought battles we shared, he messaged me and said he was going to aim his ships at his neighbor that broke a peace treaty and if I wanted to follow his ships, I could grab his stars. We were both smaller players in the game because our conflict lasted so long and produced no results, so our combined size didn’t put me ahead of anyone. It simply helped me make it to the final 3.
So I guess I feel it is very situational. Be good at diplomacy so when it happens, you aren’t on the side that gets the ships rather than the stars!