Store everything in one table or multiple tables

Possible duplicate of Storing data in PostgreSQL: One table or two? and probably to broad question.

But anyway.. Im a noob in general at database administration. I want to weekly copy data from mssql database to postgres, about 30 tables. Then use postgres data as input to power BI etc. to see trends over time. To create the power BI reports etc I will have to join tables together.

Is it best in the long run (for each of the 30 tables) to append data to existing table and add a date (I would then have to include date when joining tables together):

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Or keep the tables separated:

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