The main purpose to spamming walls is to slowly take out ranged units and allowing you to phract smack an enemy. Traps / Abatis / Trebuchets have the maximum range of 5200 (5,000 for the wall unit + 200 for battle base range), even if there is only one on the walls the range will be 5,200 so its important to keep sending waves non stop.
Spamming Traps / Abatis / Defensive Trebuchet
If you are dealing with all these on the enemies walls, you are best of sending 100 cavalry and 100 scouts. The scouts will hit the traps while the cavalry take out the trebuchets and the abatis. These are the minimum numbers to send if you want to lose as little as possible when taking out these defences.
If you want to raise his honour while taking out the traps etc, send 1,000 of each unit
Spamming Archer Towers
Sending naked archers (archers by themselves) will ensure trade fire with the opposing archer towers. If the enemy has a full compliment, between 10,000 and 15,000 on his wall you will have to send a few 50,000 archer waves at him if he has a strong hero defending. If the enemy has a low hero inside then 1 wave should be enough to move onto the next stage. As the enemies tower count goes down you can send progressively less archers in each wave. And when he has only a few towers left send only 1,000.
You can spam out cavalry units with relative ease from the enemy. Sending warriors and pikemen at your enemy will decimate the cavalry. Cataphracts take slightly more but in terms of losses, its much more costly for the person in defence losing the cavalry than you losing warriors.