I understand that the correct practice is to make a calendar for weather affected activities and use that calendar for accounting weather delays in schedule
But what if, instead of a delay calendar, we include a delay activity in the end and do not assign any resources to that, isnt it still the same? what is the disadvantage of that?
AACE -84R-13 - Planning for Adverse Weather
In summary not using weather calendars will miss what happens as activities move back and forth between rain seasons, also if using a single last activity any delay will delay the project even if there are no longer activities that might be delayed by rain.
Please note that the assumption that it will rain on certain days can be misleading for planning in the short run; the model will tell it might rain tomorrow and plan for no activities [rain delay activities] to happen tomorrow and will delay all downstream activities. The schedule with rain model shall be used for contract management while an optimistic model with no buffer at all shall be used for field management.
If not enough at times another schedule is needed, some call it Ghost Schedule.
Using wrong model to manage the field operations is not a good idea.
Ghost Schedule