Same with Delta Loads. In case a load failed during the night, you do not want to waste time in the morning with tasks that have to be completed before a new load can be performed. You will be in hurry, just execute the job and all should be taken care of automatically.
For simplicity, very often you will use "delete data before load" for the small to midsized dimension tables and use Table Comparison when performing a delta load into one table. This way, you can guarantee that no data is lost - maybe read twice but not lost - and does not occure twice as the Table Comparison (sorted input) Transform will update already existing rows.