So what occasions are more suitable for slippers? Generally speaking, you can dress as you like in private occasions, such as parties between friends, rest at home and travel. It doesn't matter if you dress as you like. But once to some formal occasions it is best not to wear sandals, such as work, class and so on.
When attending graduation ceremony, International Conference and exhibition, never wear slippers to go out, which not only makes you look sloppy, but also disrespects others. Some places even expressly stipulate that people can't wear such shoes to enter, which shows that people still have certain resistance to some casual dress.