I haven't been there and can't offer a definitive answer - even when I lived in Ontario, I was a far ways away from that part of the GTA - but I have some input..
Three aerials? Is it maybe headquarters, a maintenance shop, or are some of those actually 'quints' (pumpers that happen to have an aerial on them)? Stations are more likely to have multiple pumpers than multiple aerials.
Could some be reserve units or spares? Where I live/work these days, we have many stations which have spare pumpers, aerials, etc., parked there because that's where we have room to put them.
"Workload balance" isn't generally an immediate concern in the fire service, IMO. If an emergency is reported, you want the closest crew going, period. Here, they used to do that sort of thing with select stations, where two pumpers were in each - leaving one pumper "untouchable" until the other one was sent out on a call, and only then they could be used. Since our response for a typical building fire is two pumpers, and aerial, and a rescue, that meant often the "untouchable" pumper was left in station while another, more distant pumper, served as the 2nd in rig. That was squelched a few years ago, when the pumpers finally became "touchable" and now go on all calls.
Sorry for the ramble - but maybe some of it is the reason that station 81's full complement doesn't go on every call.
