Best Practices

List<Account> lstacc=[Select Id from Account limit 10000];
Set<Id> setIds=new Set<Id>();
for(Account a:lstacc){ //More CPU time for sure due to looping 
   setIds.add(a.id);
}


//Using Map query saves CPU time 
//Fetching all account in map
Map<id,account> aMap = new Map<id,account>([Select Id,Name from Account limit 50000]);

//Creating list of accounts
List<account> accList = aMap.values() ;

//Creating set of ids
Set<id> accIds = aMap.keySet() ;