Hi assuming we are importing the data from Excel, what would be the advantage to have the conditional columns made in PowerBI vs in Excel ? thank you

Power BI is your data viz tool. It is powerful enough to do everything Excel does and more. If you create the custom column in Excel you will have to maintain it inside Excel and then refresh inside Power BI. If you do the transformations inside Power BI everything will be in one place.

thank you for your answer. I'm worried about memory consumption. following the training I feel it looks like adding calculated col is not a wise option. with this regard, would it be better to do the columns calculation in excel rather Power BI ? thank you

it all depends on the use case, in what context are you looking for adding a calculated column? In general more columns mean more memory, so measures should be used instead of calculated columns, but if you need a calculated column for a key or to make a date or to build a text column that is the only way