Meanings
Usage patterns
〈人〉が控えに回るfor someone to be benched / put in reserve
Because of his injury, he was benched for the next match.
控えの状態で待つto wait on standby
I was waiting on standby until my name was called.
控えとして〈物〉を用意するto prepare something as a backup/spare
Just in case, I prepared an extra battery as a backup.
〈事〉の控えを保管するto keep a copy/record of something for one's files
I kept a copy of the contract on file.
Expressions
控えの間anteroom; antechamber; waiting room 控えを取るtake a copy; make a copy; take a note