SPO follows an initial public offering and represents a new public offering of securities by a company whose shares are already traded. It is important to distinguish between two cases, as the consequences for investors are opposite.
If shares are sold from existing holdings of current shareholders, the number of securities in circulation does not change and the stakes of other owners are not diluted. The proceeds go to the selling shareholders, not the company. Such an offering typically increases the free float and improves liquidity.
If newly issued shares are placed, the company receives the funds, but the total number of shares grows, and the stakes of existing shareholders are reduced if they do not participate in the offering. Per-share metrics decline unless profits grow proportionally.
From this comes a practical approach: when learning of such a placement, first establish who is selling the shares and where the proceeds go. The placement price is usually below market price, and the offering puts pressure on quotations due to the increased volume of shares on the market.