Like others have said, it really depends on the style.

Recently I've been making a lot of tech and minimal house, and repetition is key to give it a steady, "rolling" groove. This is even more important when performing live, especially in a clubby environment. When performing, a good trick is to have a distinct pattern which you can revert to at anytime. If you're feeling adventurous, switch it up! But keep your tempo steady so that you can go back to same groove whenever you want.

As for producing, another trick I like is to make slight variations rather than adding whole new elements. An extra hi hat beat in a pattern can keep a groove remarkably fresh, even if you did not change much.

Interesting question about repetition. I like techno and minimal, genres that are all about repetition but... the repetition isn't static.

Although a groove, a certain pattern is repeated, you sould add variation with filters, envelopes, adding white noise,...

Someone refers to Richie Hawtin (I love his music) and yes, it's all about repetition but don't be deceived, the movement in his music is always dare. Repetition without movement is boring, no matter which great artist created it. The art is creating something that 'feels' repetitive but in fact it isn't.

Th devil is in the details; automation of the cutoff point of a hihat sample will not be noticed by many listeners but it's stuff like that, that aks you go 'It's repetitive but not boring, how come my music isn't as interesting as that?'

Best advice I can give; create a groove and take a good look at the knobs of your synth, imagine which functions you could automate. Basically if you are creating minimal music and there isn't any automation going on, that's not a good sign. People always expect variation. Some kind of predictable change.

Richie Hawtin's music isn't about surprise but movement is there, always.