Not every episode, but there are a lot of important episodes particularly around Ahsoka and some of the other minor characters like Saw Gerrera, Asaj Ventress, Cad Bane, etc. Probably Hondo will be relevant at some point. He's not my favorite but a lot of fans love him.
Also Rebels. It starts out very kid-oriented, but after the first season it gets into some mature storytelling and continues with many of these side characters and the central characters of Ahsoka.
Other than Saw, I don't think any of it is relevant to Andor (and I wouldn't say the Saw stuff is super important to see anyway).