So slow in the United States say slow approach or slow clear. Here in Canada the equivalent CROR would be slow to stop, or slow to clear.
Those rules basically would be proceed at slow speed (usually 15MPH) through switches and prepare to stop at next signal or continue at track speed depending on the signal above. Of course there are others like slow to slow, slow to limited, clear to slow, etc. etc.
Restricting usually is the same for both sides of the border. It is also often used when getting out of CTC and entering dark territory, a yard, or even a siding that is not bonded or detectable by the dispatcher or signal system.
The rule is identical to RULE 105 territory under CROR in which you may proceed at no more than 15 MPH to half the distance of visibility, or an obstruction.
So the idea behind 105 or dark territory is it's up to the operator to restrict their movement to not run into another train or derail due to a switch etc. This is often used for return to train functions and I believe switching features. Switching features in Canada at least CN allow a crew to continue to work a yard and pass by a control point without bugging the dispatcher for a light. It's like a fleet mode (automatically clears) to allow movement and switching to continue.
Hope that helps.
Thanks
Sean