Apex トリガー覚え

Suppose you have a custom object Custom_obj__c

Trigger.New means it is a List

and

Trigger.NewMap means it is a map

順序があるか、無いか。
ループでidの一致を判定するか、idで直接読むか
https://salesforce.stackexchange.com/questions/104274/difference-between-trigger-new-and-trigger-newmap

What to use depends on what you're doing - if you have an ID of an object you need to do something with, using the map makes more sense as you can use newMap.get(). Otherwise you'd have to loop over all the elements in Trigger.new and look for a matching ID. Similarly, if you have multiple loops over each item the trigger is operating on, the list returned by Trigger.new may be the better bet.