Hi @rit372002,
Unless you really understand the impact of a bi-directional relationship AND there is no alternative then be my guest and use it. In all other cases don’t. Two main reasons are ambiguity and performance.
Mark as Date table is a best practice.
This will validate your Date table but more importantly prevent the creation of those hidden auto date/time tables that cause bloat of the model - otherwise for each date field in your model a separate hidden date table is created for you. If you have 14 date fields you get a free bonus of 14 hidden date tables. So when you see that suffix .[Date] appear for example you know you have hidden date tables in your model…
Another important reason to mark as a date table is if you want to use DAX time intelligence functions.
Read up on it here.
I hope this is helpful.