You can also beam to your bridge at any time if you want to go AFK. You won't be travelling, but it is a guaranteed "safe zone."
I probably just warp out of the DSEs more often than I stay and fight, but even so, I like that there's a chance to be attacked while travelling to my destination. I think it helps with immersion.
Of course, I wouldn't complain if the DSEs were fixed so I wasn't immediately attacked by 8 battleships, leaving me at 50% hull before I can even clear my bridge officer's message informing me of the attack. And beefed up rewards are always nice, too.
When the DSE is already triggered, and there's that little swirly portal thing with tiny ships floating in it, there's a simple dialog that went something like:
Tactical Officer (or First Officer): "Captain! There are Federation ships engaged with the enemy here! Shall we join the fight?"
Option 1: Yes, join the fight.
Option 2: No, we have more pressing matters to deal with.
Why can't they do that for the ones that chase you around, too? That's fairly immersive!
I. for one, don't mind DSE's. If I get sucked in, no biggie, that is just the opportunity to complete the dse task that starfleet has set before me so i stay in, complete one then hit transfer to another instance ...complete it..rinse repeat..less than 10 minutes I have all 3 under my belt and happily exit to sector.
and Jeff is right, if you severely need a bathroom , smoke or drink break...go to your bridge...you are safe there.