If dispatched with the HP valve locked closed (IAE engine), on descent you need to open the cross bleed and select bleed air off on that side to eliminate the risk of high pressure air from the other engine overcoming the low pressure and flowing into the engine. There are valves to prevent this but Airbus think the extra precaution is worthwhile.
Even if the temperature is below the icing range, engine anti ice still needs to be used in the vicinity of CB clouds, the A330 is more susceptible to engine ice in these conditions, as a couple of operators have found out, but the recommendation applies for the A320.
The increase in idle is significant with engine anti ice on and selecting it on the ground may cause the aircraft to move forward. Likewise on descent, keep a careful eye on your profile, particularly if using a high cost index as you will have little margin to increase speed if getting high.