They do. -taH is the general progressive aspect. -lI' is the same, except it is used when there is a known stopping point of the action. In the Klingon sentence above, the implication is that the doctor is making progress toward the known stopping point of having saved the patient. The use of -lI' is always optional; -taH can be used whether or not there is a known stopping point.
I think this is the post you are saying you erred in. But I will address it anyway. I don't know that it is quite correct to say that -lI is always optional. In just the right circumstance, it is the only way to get across specific information and so would, in a way, be required, rather than optional. However, if those specific details are not important in your communication, then you can choose to include them or not. In the case of this sentence, I might use -taH if I instead wanted to emphasize the "ongoing" nature of it rather than the "towards an end goal" nature of it. It would make it sound like the doctors actions seem to be going on forever, rather than getting closer to the goal. And if I just left the aspect markers off altogether, as in SID toD Qel it makes it sound like something the doctor does on a habitual basis rather than something that he is doing right now.
Using -taH instead of -lI' does not obscure any possible end goal; it does not emphasize continuousness over end goal. It just doesn't mention whether there is an end goal. -lI' means exactly what -taH means with the addition of the sense that there is an end goal.
For instance, if I wanted to get across the idea of an end goal, but for some reason I wanted to avoid the use of -lI', it would be perfectly valid to say something like jIlengtaH; ghochwIj vIpawDI' jImev I am traveling (ongoing); when I arrive at my destination, I'll stop.
But you'd only do that if you weren't allowed to use -lI'. Normally, you could just say jIlenglI' and the idea of reaching a destination is implicit.
The same holds for the difference between -ta' and -pu'.
He destroyed himself.
He destroyed himself (and that's what he set out to do).
The -pu' version doesn't emphasize the perfectiveness of it over the intention to do it; it just doesn't mention whether there was any intention.
Yes, you're right, jdmcowan - this is indeed the one I erred on; I finally came across the sentence again! I meant to ask about the use of the suffix -ta', not the suffix -lI. (For some reason, I was getting -ta' and -lI mixed up in the early days, but I think I've got them down now.)
Thanks for answering anyway, even though that wasn't precisely my intended question. Here's a lingot for your (ongoing, intentional) efforts! :-)
Here's an extra note for you (because I know the aspect markers get confusing)... The ongoing aspects don't care about intention, they care about end result (is the action moving towards a result or just moving?). It's the perfective markers that care about intent (and agree with each other that since the action has ended, result is a forgone conclusion).
The ongoing efforts are intentional, but I don't foresee any end goal to them.