Making units. Or researching units.

I could make ten LT.

Also this seems off-topic.

Only mods can do that. Doesn't matter interesting question tho

i will use those for researching.

Speeding up long research or unit production.

Build industries from the very beginning, plus one level 3 tank factory and/or one leve 3 artillery factory to churn defense quickly if I am attacked.

No need to buy units directly, with extra industries you have a massive advantage on the long game.

Get LVL 5 industry everywhere.
Then easy streamroll

Well, I would save up the gold for a while, at least until you have researched heavy tanks, commandos, paratroopers, and sp artillery. Wasting them on day 1 to spend on armored cars and infantry is a waste, use them for researches later on, maybe producing units in the face of an invasion which you don't have enough defenses for (say you launched invasions on Poland and France as Germany but then realized Italy and UK are teaming up against you), and sometimes to buy resources, but only if your economy is completely crippled with your resource levels going down to a negative.

I would use them for getting resources early on to start snowballing.

Produce many troops to get a boost

I would also use it for building industry but I would wait until day two or three when your resources start to get scarce and spend the gold to initiate construction on more industry without the resources. Especially for metal, oil, and rare materials since these are the resources you need for more industry as well as many of the better late game units.

it’s also worth spending a little gold, just before day change into the second day, to speed production of level two industry for metal, oil, and rare material. The production rates don’t recalculate until day change so rushing production sooner isn’t as cost effective.

Really ? I did not know this. Smart move then yes.