Hi,
depending on your application use case it might make sense to do a code-pushdown, i.e. use an AMDP.
Let me explain "depending" in two small/bold examples:
1. You have a lot of data. You fetch it from the DB into an internal table, you do a lot of calculations on the data (maybe even followed by certain aggregations), and finally you finally persist the data back on the DB or you only display a small number of records on a UI. In this example, an AMDP certainly is worth the effort.
2. You have a lot of data (or you don't have a lot of data 
) and you need the data on the application server - you didn't fetch it from the DB just do calculations (as was the case in the previous example). After your calculations you need to transfer the data further to another application (e.g. you pass the internal table) or you want to display all data on the UI. In this example, you wouldn't benefit that much from an AMDP.
So it really depends on your application/development scenario. But it's a priori not just faster to use DB temporary tables in AMDPs instead of working with internal tables.
Cheers,
Jasmin