In pickups, the amount of pipes I use largely depends on the flags location. On destroy, for example, if the flag is still in security I will 8 pipe the flag (but recently i have been experimenting with piping flag and button at the same time
).
When the flag is moved up to the foyer however, since there is a constant rush of enemies, I usually won't have time to put 8 pipes on the flag, so I usually use 2 pipes and lay down more when there is a cease in the action.