Hello, 

Well I kind of see your point but you can already call an Activity from a Data Page so nothing stopping you to Obj-Open-By-Handle

You may use OOTB like pxGetCase or OpenByHandle as well.

Hi,

If you look at the data retrieved via Look Up and Obj-Open-By-Handle, it seems the same.

But, apart from the content retrieval, Obj-Open-By-Handle method provides you options to perform actions on the instance after it loaded onto a page like save/delete and even you can lock the instance.

However, Lookup is basically helping you to look into data base and get a copy (image) of the data instance rather than giving control to that instance to do actions on it.