What are the benefits of both of these and why should they be done?
Thanks
long answer
PRAM stores certain system and device settings in a location that Mac OS X can access quickly.
Exactly which settings are stored in the computer's PRAM varies depending on the type of computer as well as the types of devices and drives connected to the computer.
Parameter RAM is a small area of non-volatile RAM (NVRAM).
[Non-volatile random access memory (NVRAM) is the general name used to describe any type of random access memory which does not lose its information when power is turned off]
Some information stored in PRAM includes:
Display and video settings such as refresh rate, screen resolution, number of colors
Startup volume choice
Speaker volume
Recent kernel panic information (if any)
DVD region setting.
thus you are resetting these to factory defaults, and together with 'repair permissions eliminates any conflicts your Mac may be experiencing or which are building up and thus slowing the Mac down.
(someone else maybe able to explain this a tad better)
Repairing permissions involves checking the permissions of a set of files and folders on a volume with Mac OS X installed against a list of correct POSIX permissions, and correcting any discrepancies.
[The list of correct permissions is compiled by consulting the various bill-of-materials (.bom) files. Typically, these files are stored within reduced-size Installer package (.pkg) files in the Receipts folder in the local Library folder (/Library/Receipts) on the volume being checked. Whenever a user installs software that uses the Mac OS X Installer package format, a bill-of-materials file is created which can be consulted for future permission repair.]
short answer:
after performing these actions one usually (though not always) notices a snappiness not hitherto experienced since the last time these maintenance actions were performed.