I Wish I Would Have Known #9: Delete Button not Available for Business Rules in PowerApps Maker Portal

Not sure if I am missing something but, I couldn’t find the delete button in the PowerApps maker portal whereas, it is available in the classic UI.

PowerApps Maker Portal

Classic UI

I Wish I Would Have Known #7: Email Tracking in D365 using duplicate email address

If you are using email tracking and your system has records that share the same email address then, emails will be tracked to all records that uses the same email. You need to consider this when designing your solution…

I Wish I Would Have Known #3: Quick Create Forms

Although you can define multiple quick create forms, only one quick create form can be used by everyone. The form everyone will use is set using the form order. Quick create forms cannot be assigned to security roles and they do not provide the capability for the user to switch forms.

https://docs.microsoft.com/en-us/powerapps/maker/model-driven-apps/create-edit-quick-create-forms#create-a-quick-create-form

I Wish I Would Have Known #1: Fetchxml VS Query Expression

It totally depends on your plugin style: In case for early-bound, I like using LINQ because it’s strongly typed and It helps development speed. Certain benchmark test have proved that Fetchxml is slightly faster than QueryExpression.

As per Microsoft official docs, there is no visible performance difference but just a personal preference of the developer.