I have mine installed on my new PS3, my old fatty (may it rest in peace) didn't have the space. I notice a big difference, but it may also be since they fixed the loading times, everything is now running much faster.
I'd say yes as im not certain on this but not installing might put extra strain on the Blu-ray since it will always have to read the disc to install when your loading somthing.
Yes The HDD is used as a temporarily storage space even if you don't install. GT5 installs race data to the HDD thats why you get the flashing install pop up on the bottom right.
It stores data for the race in a reserved HDD space. That it made the first time you ran it.
If you turn this off in the options menu it will skip all temp storage and use the BD and Patch data Only this makes for a very active BD drive during the race.
If you install data to HDD most of the common data will be perminantly on the HDD and not needed to be accessed from the BD.
As posted before Only the common data will be installed in one lump do some thing not important. and it will again install more data in case you need to repeat it again and again.
Like Jeff gordons nascar events or more menus. The first time you ever use a new car its data is then permanently on the HDD.
