What Venus does in a chart
Venus is the part of the chart that answers one question:What do I find beautiful, and how do I show affection? It describes love style — not events, and not outcomes.
What Sagittarius does to it
Sagittarius is a fire sign, so it moves on impulse and enthusiasm. It is also mutable, which means it adapts things. Put those together with Venus and you get loves as an adventure — roaming, candid, hopeful, applied specifically to love style.
Sagittarius is ruled by Jupiter, so this placement tends to be coloured by growth and belief as well.
The useful version
Placements are not verdicts. This one describes a default setting, not a limit — the things listed above are what you do when you are not thinking about it, which is exactly why noticing them is worth something.