Using "New by contact" allows you to enter quickly a transaction from selecting a contact (you've previously saved).
This insertion is very useful and fast as to each contact, you can assign a category, a payment type and a default account, in this way, you will create a transaction with all those default settings.
Do not you want to include all the default settings for all your contacts?
Do not worry, MONEE will do it for you. When you enter a transaction and then a contact, MONEE will save the category, the account and the type that you used as default parameters to the contact.
For example, I create an expense of € 15 on the contact "Restaurant xxx", choosing as category "Leisure" and as account "Cash". MONEE will save them as default setting for the contact "Restaurant xxx" indicated in the transaction. You can track the next expense made at "Restaurant xxx" by selecting only the contact, and the amount spent!