On your other question, you mention SB910s and CLS, so I'm going to assume you mean using CLS's slave mode, vs. manual PocketWizard radio triggers (like the PlusX units); and not "dumb"/SU-4 mode, or the flex/mini TTL-capable PocketWizard triggers.

The main advantages are range, reliability, and no line-of-sight requirements when used outdoors in bright light.

Optical slaving requires that the optical sensor on the flash can "see" the master signal from the camera. That means you can't put the flash behind anything that will physically block the light from reaching the sensor. And in brighter light conditions (sunlight outside), the master signal is relatively weaker to the ambient light). And without bounce surfaces around, the line-of-sight requirements become more stringent. Radio doesn't have any direction requirements and can be used over much longer distances, and (obviously) isn't affected by ambient light conditions.

The main disadvantages with manual radio triggers, are a lack of remote setting controls and features like TTL and HSS/FP.

If you're using manual radio triggers, however, while you gain on reliability and range, you can lose a lot of features that CLS offers you--TTL, HSS/FP, remote power control, etc. etc. These are all features that CLS supports that a manual radio trigger can't. TTL radio triggers (like the PocketWizard Flex/Mini units) can. So the differences become smaller if those are the units you're talking about. Manual units, like the PlusX can mostly only relay the "fire" signal.

Also understand that the SU-4 slave mode is manual-only and optical, so with it you don't have any of the fancy features and all the vulnerabilities of an optical system--but it's more universally compatible and could be used with, say, a Canon setup.

And some flashes, like the Canon 600EX-RT, have radio slave capability built-in that does pretty much most of what CLS can do, but over radio. So your question can be answered in a variety of ways. :)

On your other question, you mention SB910s and CLS (Creative Light System), so I'm going to assume you mean using CLS's slave mode, vs. manual PocketWizard radio triggers (like the PlusX units); and not "dumb"/SU-4 mode, or the flex/mini TTL-capable PocketWizard triggers.

The main advantages are range, reliability, and no line-of-sight requirements when used outdoors in bright light.

Optical slaving requires that the optical sensor on the flash can "see" the master signal from the camera. That means you can't put the flash behind anything that will physically block the light from reaching the sensor. And in brighter light conditions (sunlight outside), the master signal is relatively weaker to the ambient light. And without bounce surfaces around, the line-of-sight requirements become more stringent. Radio doesn't have any direction requirements and can be used over much longer distances, and (obviously) isn't affected by ambient light conditions.

The main disadvantages with manual radio triggers, are a lack of remote setting controls and features like TTL (through-the-lens flash metering--an automated way to set the flash's power) and HSS/FP (high-speed sync/focal plane flash--being able to use shutter speeds higher than the camera body's maximum sync speed).

If you're using manual radio triggers, however, while you gain on reliability and range, you can lose a lot of features that CLS offers you--TTL, HSS/FP, remote power control, etc. etc. These are all features that CLS supports that a manual radio trigger can't. TTL radio triggers (like the PocketWizard Flex/Mini units) can. So the differences become smaller if those are the units you're talking about. Manual units, like the PlusX can mostly only relay the "fire" signal.

Also understand that the SU-4 slave mode is manual-only and optical, so with it you don't have any of the fancy features and all the vulnerabilities of an optical system--but it's more universally compatible and could be used with, say, a Canon setup.

And some flashes, like the Canon 600EX-RT, have radio slave capability built-in that does pretty much most of what CLS can do, but over radio. So your question can be answered in a variety of ways. :)