I'd prefer not to have twins if possible, but it happens sometimes, and can turn out ok.
Pros: best case scenario cow has enough milk for two, accepts both, maintains her condition, and you get an extra calf at sale time
Cons: more chance of complications calving, more chance cow will reject one and will wind up with a bottle calf that you have to raise or find another cow to put on or sell, or cow will accept both, but not have enough milk for two and will have a bottle calf or one that is a runt and won't bring much, and two calves can really pull a cow down by the time they are weaned depending on the cow