How do you use most welcome?

Excuse me, could you please elaborate on how one might effectively utilize the phrase "most welcome"? In what contexts is it most appropriate to employ this expression, and what sort of response or feeling does it typically elicit from the recipient? Additionally, are there any cultural nuances or variations in its meaning that one should be aware of when using it across different social or professional settings? I'm particularly curious about how this phrase can be used to convey genuine appreciation and warmth, without sounding overly formal or insincere.