She 'handed the reins' of the company to her successor. = She 'handed over the reins' of the company to her successor.
He has people working for him, but he 'has/keeps a tight rein on' every part of the process.
We need to 'keep a rein on' our spending. [=we need to limit/control our spending]
(..) Yeah. (sighs) (sighs heavily) Woman: ♪ ich bin klein ♪ ♪ mein herz ist rein ♪ ♪ soll niemand drin wohnen als ♪ ♪ jesus allein... ♪ (singing in german continues) ♪ ich bin klein ♪ ♪ mein herz ist rein ♪ (..)2015 TvShow: Homeland Title: A False Glimmer Season: 5 Episode 12