I always play w/o surrenders, I used to get so annoyed when i'd start a war with an empire almost as powerful as me and as soon as you took a couple of planets or destroyed alot of their ships, they'd surrender to a more powerful race i'm at peace with, thereby making their planets unattainable, then... due to the increased power the larger race gets from those extra worlds, its only a matter of time before they declare war on me for no reason.

I've never seen them surrender to me during a war, but I have had it once where a race I was on good terms with gave all their stuff to me when they were losing a war, so I guess its a double edged sword

better without IMO

and I always play with surrenders on. I think it gives a bit of the unknown to the game but it really helps with the grinding down of an empire. You may get them to surrender without having to send as many transports. The rate at which you may get surrenders differs, some races never surrender and will lose their last planet. But it seems from the other posts that in TA the AI gives up a lot more easily. For the most part, in DA its not so easy.

It seems to be ramdom as to when and to whom a race will surrender. I think your alignment as compared to theirs has a bearing on what ships you get from them even if they surrener to someone else. An evil race's left over ships will become pirates. There has been a lot of speculation about this but no one has come up with any concrete answers. And its better that way.

What i think many people dislike about surrenders is that theres a chance that the race you are fighting will surrender to someone else. And that somone else could be someone you do not want to have extra planets and ships. However, I like the

So, I would suggest that you play with them on, you may wind up gaining a few planets from a race you weren't even at war with... or not. Who can tell?

I always play with surrenders on; it adds an extra layer of strategy, detailed below: 

What if Race A Surrenders to Race B?

Should I ally with Race B, then go to war, letting Race A build up,

 or take the chance and attack Race A right now?

And it (usually) ends wars before they become "useless", i.e.,  no wasting time mopping up far-off planets and straggler ships.

I turned it off after a game when the AI surrendered (IIRC Thalan) without losing a planet and transports were still a way off on the tech trees (for everyone). It was "very early" in the game!!! I saw no reason for it and decided to just stop using it.

The reason the Surrender on/off feature was added was due to feedback originally from DL. The AI would just surrender with 30 planets or more at times all due to a perceived inferiority in military rating. If you were putting up a bogus rating using the SCC or Starbases the AI would surrender in a situation they could of won.

I'm now playing a DA game where the Torians fell, losing their last planet, never surrendering. The Terrans JUST surrendered (with only 3 planets left, after having nearly 20) but not to me, even though i built that Good-only structure thats supposed to double the chances that a surrender will go to you if one does occur.

The Arceans should have surrendered long ago but still hang on. I never fought with them but the Drath and Kryyn had them down to just 2 heavy fighters at one point. And most of their planets are gone.

I like long games, so I haven't gotten to play that many under each expansion and updates, but my overall impression is that they are currently less wacky than I've seen them in the past (I'm pretty sure we've had at least two spikes of wacky surrender behavior).

I've lately seen both some "Surrender, already!" and "You did what?" situations, but the latter has become more often about who gets the surrendered empire, not when the surrender decision happens. Either the choice is very random, or there is some funky decision code under the hood.

Re the OP's question, I'd say newer players might want to leave them off (along with events & mega-events), but after that you need to have several games with them enabled to see whether you find them generally fun or generally annoying. It's a taste thing, like the events.

I'm curious, though, about whether there's a strong consensus for or against the feature amongst the scoremonsters. If piling up points is your goal, are you better off with the bitter-end dynamic you get with surrender-free games, or is it somehow overall better for scores if you start with 10 majors and let the weaker ones fall after doing some scut work laying down colonies for 'the real powers' to take over?