Should I do the new iPhone update? Or is it pointless?

Does it delete anything? Is it a bad idea to do this?

It will not delete or modify any data in it, apart from upgrading to new operating system.

Though it is highly recommended to do a backup of your iPhone before performing any iOS update. This can be done either by iTunes or iCloud. It may also takes a while if this is your first backup or if you have not performed latest backup for some time - and also depending on the used capacity stored in iPhone.

I don't see why not.
No it doesn't delete anything.
Why would it be a bad idea to be up to date?

It was for me - the original update, iOS 8, downloaded but failed to install properly and threw my phone into recovery mode. It took 40 hours to restore it as the software wouldn't download and then when it did it wouldn't install as iTunes suddenly decided my phone did not exist. I think I'm on first name terms with half the Apple Support crew. I eventually managed to download iOS 8.0.2 but I don't see what's so great about it and I don't like the way they've removed the camera roll album from photos or the ability to delete apps that came with the phone.

Wait 3 weeks, thats what I always do. I want the new version but I like to see a few patches come out first before I update it. I waited about 2 months when iOS 7 rolled out and that ended up being a great move.