There are no limitations to NOT using derived fields apart from the nice organization on the left side. There are a few more limitations to date & time fields (derived fields) that can make it work just keeping the field as is . For example, derived fields have not been yet supported in set analysis .
Re: DateTime not recognized as Date & Time from SQL Server - Qlik Sense 2.0
I have the exact same issues. I did not work with the Data Load Editor as I am a beginner but I am using the Data Manager.
I have 3 tables residing in the same sql db. All 3 have a column called [Week] which is under the SQL datetime format.
When I'm loading the tables, I see very chaotic and random behavior: in 2 of my 3 tables the date shows up in the correct date format, but in the 3rd one (the largest one) I get either serial date (5 digits excel format) or YYYY-MM-DD HH:MMS but not recognized as qliksense date format, but as general.
To make myself more clear - If I upload the table one time the date shows up as serial date. After I delete the table and reload it, it shows up as General and so on.
I know you are going to tell me I need to control this in the Load Script Editor. I don't want to since I don't understand why identical columns in SQL are uploaded differently...