Piazza San Marco is the main public square in Venice, the very heart of the city. In the square you can find impressive historic buildings like St. Mark's Basilica and the Doge's Palace. The square has been a focal point of Venetian life for centuries. Here you can find shops, restaurants and cafés, including Caffé Florian, the oldest café in Italy dating back to 1720.
Piazza San Marco is full of people day and night and it can be honestly hard to enjoy it. Most people won't wake up early or many cruise tourists won't even be in Venice early in the morning. Well prepare for one of the best experience to do here, having St Mark's Square all for yourself! From 5 am (only in months when there is early sunrise) up until 8:30, the square and Venice overall is completely empty. I did this twice and it's the best thing, especially if you love photography and want to take great photos with amazing light. But also if you just want to enjoy the place, go early. I'm definitely not a morning person, but having a place that is often so crowded you can't even enjoy it all for yourself is the best.
Definitely get it if you don't want to wake up super early, but try to go before 9:30 anyway, it will be a bit less crowded.