There are two types of grounds...
- True-Ground (Normal ground, all metal components touching.)
- Isolated-Ground (What is commonly called the "-12v, -5v, -3.3v rails" or "common".)
Not all PSU's are created equal. Some use the "Ground" as the "Common", without isolation. (Ground-loop isolators.)
It does not matter how many "points" you have, as long as you have ONE point that is low-resistance. (Copper wire) Adding more points will help to ensure that you are adequately shielding RF noise, from both emanating and absorbing it. There is no "issue" of "ground-looping", through the high-resistance "STEEL-ALLOY" cases. (Unless you have faulty or ill-speced equipment and wires.) You do guarantee that the potential damage from shock, or accidental "short-circuiting" is limited, with correct grounding. Without it, you just open your system up for potential harm and damage.
Can you live without ground connections... Yes.
Will you damage anything without them... Not just by the absence of them.
What will happen without them... Slightly more "noise" in your AM/FM radio, and your CFL lights may "disrupt" some high-speed data-lines, but those will auto-adjust. Plus static-sounds and pops or "whines/humming" in your sound-card/speakers.
What is proper and safe, is to encase the entire unit with the ground, with multiple connections to that ground.
Ground points on a computer...
- The PSU case/screws
- The tower case/screws
- The mobo risers/screws
- The card mount-plates/screws
- The "common" wires on all DC plugs
- The hard-drive case/screws
Electricity takes the "path of least resistance", thus, most "ground/common" power will ALWAYS flow through the low-resistance copper wire. However, ESD and RF don't care about resistance, and often travel faster across high-resistance surfaces. (Plastic/skin). That is the "purpose" of ground-shielding and ground-isolation. (Ground-isolation is just higher points of added resistance, ti "ensure" that the lower-resistance is traveling where it is more desired. In the event of over-loading, additional GROUND -volts, will be allowed through any isolated connection, which is desired, to reduce damage/fire/heat/wires.)
Low-resistance - High-voltage things...
- Spark-plug wires (98% resistance, glass-insulated.)
- Capacitors (The inner plates separated by insulated material, glass, plastic, air, oil.)
- Van-de-Graaff generators (Rubber/leather is the "source" and the highest resistance.)
- Wimshurst-influence machines (Ebony or plastic or glass is the "source" and highest resistance.)
- Trees, you, diamonds or anything organic with a carbon-base... but not carbon itself, which is low-resistance, with the ONE exception for lattice-diamond-structures. (Carbon fibers even have "apparent" negative resistance.)
http://www.wings.buffalo.edu/academic/department/eng/mae/cmrl/Apparent%20negative%20electrical%20resistance%20in%20carbon%20fiber%20composites.pdf