When can you say welcome?

Can you elaborate on the specific context in which the phrase "when can you say welcome?" might be used? Is it in reference to greeting someone upon their arrival, welcoming them to a particular event or occasion, or perhaps acknowledging their presence in a new or unfamiliar setting? Understanding the broader scenario would help me to provide a more accurate and contextually relevant description of when it's appropriate to use the phrase "welcome." Additionally, the tone of a questioner could vary depending on the specific situation and their intentions, ranging from polite inquiry to genuine curiosity or even skepticism.