It is honestly mostly for looks. It is a lot harder on the hub (not a problem if you are running brakeless, but even rim brakes can mess up a cheap hub if it is radially laced)

It is slightly lighter, slightly more aero, but overall the difference is negligible.

I think there are also some hubs that you will void their warranty if you radially lace them (phil wood hubs make a big deal of the fact that radially lacing the hubs won't void their warranty)