"load-interval 30" is simply to change the interface statistics to display a statistical exponential average over a period of 30 seconds instead of the default of 5 minutes. Simply put, it averages the input/output packet rate over a period specified in that command. There is no impact on the actual data traffic flowing thru the switch/router nor any performance degradation. So you are free to use it and change it to any value you like.
Typically for troubleshooting, we use the lowest value on the interface to give us a more accurate 'instantaneous' value of the rate of the traffic. But there is no rigid 'guidelines' or recommendation for it as such.