The thing about golems is that they are
super risky to use. For players playing well below their skill level (or using cheats), who just want to have a fun romp and want to see a lot of massive destruction, golems are an obvious choice. For serious players playing at or slightly above their skill level, golems are dangerous; enough so that a lot of the advanced players avoid them.
To be perfectly honest, this is by design: if golems were too easy to use at the higher levels of play, then the game would devolve into a race to get them, and everything else would lose value by comparison. Look at a late game of SupCom: in my games, the experimentals were so powerful that a single flying saucer could win an otherwise unwinnable scenario -- by itself.
I am sure that some of the advanced players will shortly tell you that golems are not strategically worthwhile. This is not so (although, for a few like the Cursed Golem that might be true). But for a black widow, I've personally used those to clean out
multiple mark IV planets before it died (without any support).
There are a variety of strategies for successfully using a golem, but they are far from easy to use (again, by design). Used incautiously, they can make a bad situation worse, or can even lead straight to death.
Here are some general tips:
1. Golems really piss off the AI, so make sure all the adjacent warp gates are killed before you start rebuilding one.
2. They will generally raise the AI Progress by around 100 just for repairing them once, and further repairs will cost another 100 AIP for every 75% damage you repair to the golem. And if they die, there's another 100 AIP. You must have a goal, and a strategy capable of achieving this goal, worthy of this cost before you even think of repairing one of these monstrosities.
3. Offensively: the longer you stay in one place with a golem, the worse it will do -- it causes the AI to reinforce more strongly, and in greater numbers each time it does reinforce where the golem is. It is best to have the golem go in, do its dirty work, and then move on. If that means leaving even a few hundred straggling AI ships loose as threat, so be it. Make sure you have turrets and/or a large fleet waiting to mop up after the golem; if the golem tries to do its own cleanup work, it's likely to cause more of a problem by giving the AI longer to react.
4. Offensively: again, golems are all about the blitzkrieg, preferably against unsuspecting targets. The absolute best way to use them is to strike a target that is unprepared. Generally, if a planet has been on alert for hours and is hugely reinforced, the golem is going to take more losses than it should at that planet, simply due to the amount of firepower that is concentrated on it. You can use a golem in this way, but the fast-strike-followed-by-other-ships-mopping-up strategy is again the way to go. That's a lot of AIP cost for one planet, though; it's cheaper just to nuke the thing unless the planet is filled with Mark V ships (and even then, there are cheaper things to do). Most golems are better used to cut a huge, immeasurably-damaging swath through a bunch of semi-defended AI planets. Nothing else can sweep through so fast and so effectively (a few of the more specialized golems are even more challenging to use, though).
5. Defensively: keep your golems away from any planet with warp gates, and you'll be able to use them as a pretty incredible defensive structure for no permanent cost aside from the ~100 AIP cost of initially rebuilding them, plus whatever you spend on repairing them further. In most games this may not be worth the cost. But in maps where your home planet is continually at risk and otherwise pretty impossible to defend due to a plethora of inbound wormholes or whatever other factors, this can be a gamewinner. Also: it can free up the entire rest of your fleet to concentrate itself on offensive actions which can also be of immense value. Also: a single golem can often eat a CPA for lunch, depending on the golem, the size of the CPA, and how the CPA approaches your planets.
6. Do note that these are cheapest in terms of energy, AIP, and other factors if you use them offensively to do as much damage as you can before they die, and then let them die (or, if you are very quick about it, get them near the point of death and then withdraw them to somewhere safe behind your lines to just sit in storage). Continuously repairing them over the course of a long game is a sure path to a loss in most cases, as it makes the AI take
way too much interest in your goings on.
In general, the two suggested uses for most golems in advanced play are:
A) Offensive blitzkriegs that are over and done before the AI knows what hit them.
B) Defensive bulwark away from warp gates, guarding a key target so that the rest of your fleet isn't trapped on guard duty.
Hope that helps!