The phrase conveys warmth and approval, used when someone's actions or character makes you feel good. After she helped me with my project, I realized she's sweet.
Pro Tip 2/3
Subtle Compliment
Often used to compliment without overstating; it's a modest way of praising someone. She’s sweet, always smiling at everyone in the office.
Pro Tip 3/3
Non-Romantic
The phrase doesn't necessarily imply romantic interest. It can be used platonically. My sister is the kindest person I know; she’s sweet to everyone.