Sphereworlds and Ringworlds

[Lord Kodos]

"BTW - Is there every a strategic situation where building one of these makes sense?"
Well in LR you can build tiny uninhabitable things around your star called Stabalizers that protect it from going nova.You can always Colonize one and use it as a capital.They are mainly meant for battles of "epic galaxies are nothing to me" battles.....like most of the ones in LR.Ringworlds i find to be more usefull then Dyson Spheres.For one thing they are cheaper,require less work and yet are still figureheads of an empires massive wealth and power.You can load them up with resource harvesters and in time they will pay for themselves.You can use them as Fortress's like say for example your mighty empires under heavy attack but you have alot of credits,build one and evacuate your other worlds.Load them up with fleet training facilities and churn out the uber ships.

"It appears in science fiction literature, the only use for these giant constructions is to gift it to a neutral"

Warning Ringworld and Halo Spoilers:

Not true.If i recall in Ringworld the Pak who built it were still there but fell into anarchy so it wasent gifted to anyone.And what about Halo you can always use Ringworlds as weapons...or to store races to hard to eradicate but too dangerous to let be.