ATC Holding clearance - why holding side?
 

When ATC gives a holding clearance, why do they give the side to hold on (N, NE, E, etc)?

The side will always be based on the radial from the fix and the direction of the turns, right?

For example, Hold on the 230° Radial (standard turns) would always be the same as Hold southwest on the 230° Radial (standard turns).

Not quite. Different patterns:

"Hold WEST of the XYZ 090/20 on the 090 radial, Standard Turns." Pattern inbound course is 090, and the pattern is on the south side of the 090 radial.

"Hold EAST of the XYZ 090/20 on the 090 radial, Standard Turns." Pattern inbound course is 270, and the pattern is on the north side of the 090 radial.

That's a good point. So it must only matter if your clearance is to hold on a fix off a radial. The radial will always be 090 however your fix is 20 miles out and you can hold on either side of that fix.

In the event you are to hold at a VOR, the hold side is irrelevant since ATC will always tell you to hold on the desired radial with either left/right turns - which determine the side. For example, it's impossible to hold southwest of the 090 radial with standard (right) turns. The only place to hold would be northeast. Right?

The original question, why hold on a particular side?
The first thing that comes to my mind, as to why......... Terra Firma.....

Cumulo granite
Other airports traffic areas
Restricted areas..... The list goes on, and on and on.

Also, if there is ANY doubt as to the proper pattern, the direction may help resolve it.

It doesn't matter in a sim....

Surely, ATC will only issue such instructions if a holding pattern is not published. If that is the case, instructions may be taking account of other traffic.