They hope to make big 'gains' in Congress in the coming election. [=they hope that many more members of their party will be elected to Congress]
Her hard work 'gained' her their respect. [=she has gained their respect through hard work; they respect her now because of her hard work]
a stock that was one of the year's biggest 'gainers' [=one of the stocks that increased the most in value]
(..) Notified. That we are notified by mail to come down to this place to decide on the guilt or innocence of a man we... we have never heard of before. We have nothing to gain or lose by... by our verdict. This is one of the reasons why we are strong. We should not make it a... personal thing. (..)1957 12 Angry Men
(..) - I don't think he could have heard it. - Maybe he didn't, with all that el noise. - What are you people talkin' about? - It stands to reason he couldn't have. - Why lie? What's he got to gain? - Attention, maybe. You keep comin' in with bright sayings. Send 'em to a paper! They pay $ apiece! (..)1957 12 Angry Men