If they want to control the company, without outright buying it, yes. It’s the classic way to acomplish a hostile takeover. Thing is, buying half the shares on the market is often more expensive than the current market cap, as mass buying shares sends the price up quickly.

When buying a company outright (ie, your company actually owns the purchased company and both sides agreed to the transfer), then it is common to buy out all the shares at (around) current market value.