Do not assist large projects - you can set that value to say 100, and you engineers won't auto-assist. More specifically, you can set it to the lowest of the golem's metal/crystal cost to cut off assistance to that. I think the build times (and cost per sec) of golems was changed recently, while the total cost stayed the same. But let's say that Golem X costs 240 metal a second to build. If you put 200 in the "do not assist large projects" field, your engineers won't automatically assist that golem.
Standby works for some other things, I hadn't noticed a repair speciific cutoff or to not assist stand-down structures. I can't speak on that yet, maybe later today I will. Still helpful if you don't have engineers on FRD and want to stagger your construction of 300 turrets, you want to prevent a cloaked unit from firing its weapons, or you want your Riot Starships/Black Widow Golem to let go of tractored units so they can cower in a corner for repairs.
