I have some questions regarding two things on this page.

Delete the temp (.tmp) files in the DCCache Folder. Those load into RAM.

What are these files and what do they do? Will they regenerate? I have 8 files totaling 1.62G.

If you travel WA style you get for example a China nhd file; if you NEVER want to go back to China and don't care about any relationships there (they will be gone forever) delete the file. It is strongly suggested when deleting .nhd files you have Error Trap and Overwatch in place.

Does this apply for Uni or Oasis landing? I've sent my sims to the future and it created a nhd file and a package file. Do I delete both? And I want to keep ONE relationship from the future (because he's the father of my sim's child). Will anything happen if I move him in before deleting the file(s)?

The *.tmp files in DCCache folder is created due to opening the Launcher each time.
I think its one of EA's flops, the meaning behind this is, when you install a Sims3Pack and you don't want it, you can revert it to before you installed the S3Pack, by deleting the ones the game reads and removing the *.tmp from the files.
Though it wasn't think through enough where it used in the Launcher at all, not only that, those on Patch 1.69xxx (ORIGIN) are required to play TS3 game through the Launcher, so its rather irrelevant for those on that patch.

If you never intent to play the foreign worlds again, you can delete those *.nhd files, as for that father's child you either have to travel to the world to retrieve the Sim or use MC> Invite Over command before deleting the *nhd. Don't use the phone option.

Now you mentioned it, I do remember it once behave as such, though, like you (igazor), it wasn't often when my TS3 userdirectory was opened on the DCCache folder, so it could just be a shared dream we were in?

Deleting sub neighborhoods nhd files is pretty much good for nothing as it only affects the loading time when you first load your game. My current save game has China, France and Oasis Landing nhd files and I've moved my Sims to a new town three times yet the game play's still running fine.

Oh yes, for slower PCs, the loading screen will take longer than usual if the save game gets bigger. Mine isn't designed for modern PC games so it doesn't matter. For WA neighborhoods, I always cheat my Sims visas with DebugEnabler so I can make them stay longer so my Sims has more times to explore tombs since I never tend to go back there again for a second time. Oasis Landing is just meh and Sims University, kinda lazy to remove all the social groups hidden traits so DebugEnabler really helps me a lot

If I remember correctly it was patch 1.55 that ended the automatic deletion of the .temp files.

I feel like it was around the 1.5x patch series when they added the temp file system to the launcher if I'm not mistaken. They seem to be used to fix the issue where the launcher wouldn't show installed content after so much had been installed due to memory limits by copying the launcher data that's relevant to those files and only reading those after.

As for University and Oasis, you can delete those as well, yes. The Sim you move in should be fine.