When do we need to get our wheels aligned and balanced?

I'm switching my steel wheels over to alloy wheels and was wondering whether I need to get alignment and/or balancing done.

The new alloy wheels are bigger 16 inch

The old steel wheels are 15 inch

not really but wouldn't hurt, at least you'd know everything was ok.

balanced when you feel wobbles in the steering and an alignment if it pulls to one side or ware on the tyres is uneven.