The problem with bidding 6 infantry for Moscow is that it’s passive, long-term, and dice-dependent. In some games, Moscow will hold just fine even without the 6 infantry. In some games, Moscow is doomed even with 6 extra infantry. In some games, adding 6 infantry will give you an extra 30% chance to hold Moscow, but you will still get diced. It’s actually pretty rare that putting 6 infantry in Moscow will swing the outcome of the game. Even when the infantry are decisive, they usually don’t result in a change in who controls what territories in the early game. If you put subs up Italy’s butt, then you drop Italy’s middle-game income from ~25 IPCs all the way down to 5 IPCs, and you probably also boost the UK’s income. If you put infantry in Moscow, then you don’t drop Germany’s middle-game income at all, and you probably don’t boost the USSR’s income.
If you hold Moscow but do not otherwise stop the growth of at least one Axis power, then you lose the economic race in the endgame. If Germany is earning 80 IPCs (easy enough with Norway, Leningrad, Stalingrad, Caucasus), Italy is earning 30 IPCs (Egypt, Greece, Med, Iraq, Persia), and Japan is earning 65 IPCs (China, India, money islands), then the Axis are at 175 IPCs, and the Allies just can’t match that. You get maybe 15 IPCs from Russia, 15 from ANZAC, 30 from UK, and 80 from USA = 140 IPCs total. So it’s not enough to hold Moscow; you also have to shut down the Axis growth somewhere.
Maybe America can contain Japan and roll back Italy while UK flies fighters to Moscow…but that’s risky; you make a mistake or you lose a 50-50 battle, and then you lose the game.
If you’ve got a 20 IPC bid to play with, better to use it on something more certain, like 2 subs and a DD for Taranto (Kill Italy First), or artillery & tank in Siberia, infantry in Yunnan, artillery in Szechuan, and infantry in New Guinea (Kill Japan First). Those purchases start paying dividends from the very first turn, and they decisively swing a lot of small but important battles for high-value territories.
I have never seen the point of bids that are meant for a turn 1 attack on Tobruk. If you can win control of the Mediterranean (and with 2 subs for Taranto, you definitely can), then the Italian forces in Libya are no threat at all to Egypt. If they don’t win through to Cairo, they’re not going to do anything important. At most, they conquer 3 IPCs in French North Africa for a couple of turns before getting wiped out by Americans who would want to stop over in Morocco anyway on their way to Rome. Similarly, gaining British control of Libya doesn’t do anything exciting for you – it’s 1 IPC. People freak out over the north African campaign, but it’s just a bunch of yawning, empty desert. It’s not strategically important.
Same thing with bidding an artillery in Sudan – yes, if you really want to, you can take out Ethiopia early, but it’s only worth 1 IPC. Italy only has 4 units in East Africa, and if you keep control of the Mediterranean and Cairo, then Italy has no way of getting any reinforcements down there. The French infantry in West Africa and the British infantry in South Africa have nothing better to do than contain the Italians in East Africa, and you can build more units in South Africa as needed, and/or send the tank from Alexandria south to help out. You can pick off the Italians in East Africa any time you like – there’s really no need to rush that attack. You will collect your UK Europe on turn 1 no matter what you do, and you will miss your UK Europe NO on turn 2 no matter what you do, and you will wipe out the Italians in East Africa and collect your UK Europe NO on turn 4 no matter what you do, so taking Ethiopia early flips your NO for, at best, one turn. This is not the kind of high-priority target that justifies a bid.