You are slightly mistaken.
"Cancel Speed Restrictions" means just that... cancel the 250 below 10,000ft requirement on the SID/STAR. The height requirements still apply.
"Cancel crossing/height requirement at ....." means just that... cancel the height requirements, but the speed restrictions remain.
Airports in class C in AUS operate at 250 below 10,000ft, and this applies even when not on a SID/STAR (say under radar vector). In Aus it can be cancelled by ATC when required/requested traffic permitting. Some countries cannot cancel the requirement, and some others it only applies when on a SID/STAR... when under vectors then all bets are off.
For departures, it is usually used when an aircraft is levelled off down low, so as to not waste the level segment and accelerate (such as the MARUB departure), or by heavy jet traffic that has a flaps up (clean) speed above 250kts.
For arrivals, usually when traffic is light, or ATC want you to fly faster to fit into the sequence more efficiently.
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