I just found that I have 4 GB of space in /Documents and Settings/<user name>/Local Settings/temp
.
Is there any reason why I shouldn't go and delete these?
The location you mentioned is the default location for System Environment Variable "TEMP" or "TMP". Applications use the TEMP for storing temporary data, data that will be needed for the specific user session & installers use it to extract the data from the compressed installation files. You can safely delete any files that are not locked. (Locked files are still being used by application for storing user data). The easiest way will be using CCleaner a freeware to do it for you.
Can I delete this? What are the implications?
You can go ahead with cleaning up of this. There would be few files which are in use by Windows, and you'd error out while trying to delete them.
I'd recommend using a tool like CC Cleaner to clear up.
C:\Documents and Settings\[MyName]\Local Settings\Application Data
holds data regarding configuration files, settings, and other data which may/may not be required. I recommend you don't touch this directory.
Everything in the tempfolder should be ok to delete, some files are probably locked but you can ignore them.
Do NOT touch the "application data" folder. This is where all "good behaving apps" store their data (settings and such)
You may find yourself unable to uninstall some applications that put their .msi packages there. Other than that it's all right to clean up. Better do it right after reboot so that less files there will be in use.
Don't worry about locked files. Just delete all the files you can, and ignore the ones you can't.
I usually create the directory C:\Temp and set it in the environment variables "TEMP" and "TMP" for both the system and the user. That way, it's much easier to survey the accumulated junk. Sometimes I find files in there that I prefer to keep, which is another reason that I don't use CCleaner, etc. to automatically do it for me.
Create another folder with a different name and move the files into the new folder.
I needed this information in the past and ended up deleting most of the files and keeping a couple folders after much research. This is not the same as the Temporary Internet Files. You can delete those any time.