My first playthrough (on Normal) I did not call a single army to help. I tend to do that in video games, like if they give me an ultra powerful gun (BFG) but very limited ammo, I'll tend to never use it unless I find myself in a spot where I'm constantly re-loading a save. I'm slowly trying to untrain myself from this habit so that I actually enjoy these perks a game will give you.
But yeah, I didn't call any and walked right through the whole end sequence (level + boss) without ever calling them in. My second playthrough was on the next higher difficulty and I did call them that time, but it was more because I had zero mages in my party (sided against both Wynne and Morrigan). That was brutal and quite a fun challenge. I actually sided against everyone I could via dialogue, so my party consisted of I think maybe 5 or 6 characters total when prepping for the final battle. I forget exactly the number, but it was tiny.
The armies were quite handy in that circumstance and I absolutely needed them in two spots, no doubt.