Asklemmy

Hmmm, but that standard, I would err on it being inseparable, and mostly on the side of being a benefit.

Any complex life form needs complex environmental feedback of some kind, because if it's anything like life as we've conceived of it, it needs external energy (food in our case) and avoidance of damage (no matter how mild the environment).

Sentience is just a high grade of that fundamental concept. It's the difference between something like a plant that grows towards light and away from competitors; and something like a shrimp that makes a constant loop of processing external stimuli vs internal algorithms that predict probable outcomes.

As such, it can only be a benefit on an evolutionary level that the form of sentience become as complex as the niche the organism needs to fill/exploit that niche. A shrimp only needs a low grade of sentience because it's a fairly simple and small niche. An eagle would be a higher complexity sentience because the scale it functions in is massive and involves wider risk/reward variables, with attendant import to outcomes.

I don't think any organism will develop more sentience capabilities than it needs for long, nor will it keep it for long once a given level of need is past. If eagles all get sent to a large underground bunker, they don't need the brain power to process everything, nor the energy it takes to maintain it. You'll end up with a simpler processing of stimuli. Less flexibility, but also less "stress" from repeated decision making.

None of that requires thought though. Decisions on that scale "is a rabbit going to fight back enough that I should avoid it", where accumulated data in memory can be used to guesstimate outcomes, they don't require a conscious process, any more than us catching a ball does. To the contrary, thinking about some things makes them harder to do well. If an eagle had to think its way through snagging a running rabbit, it would be fucked.

And that's really where sentience ends: thought. When there's a "self" to make a decision based on conflicting stimuli and memory.

So I don't think sentience can ever be more of a drawback than a benefit. By its nature, it happened because it was a more successful way of surviving long enough to breed.