In the industrial world, aka where crane requirements are heading towards unfortunately, you need ratings on everything, to the point where if they become illegible, you retire the sling. I personally haven't worked with amsteel slings there yet, but i plan on getting some spliced for personal use. Ironworkers used to make their own steel slings, but even that practice has disappeared. Which is really too bad because hand spliced slings used to be a super handy tool because they are more flexible than the pressed ones.
They have actually gone so far as to remove some of the other awesome rigging tricks such as homemade spreader bars (without engineer approval, stamp, and tag), homemade gin poles and derricks, half hitches to Christmas tree stuff, and other "redneck" rigging. The older guys are the only ones who are familiar and comfortable with that skillset (and a handful of guys like me), so in reality there's a death of knowledge in rigging techniques. They even outlawed the boiler hitch on about every job too. That's where you basically use the chain from a chain fall or come along and tie a cows hitch, with the chain hook to grab the loop. You can then rig stuff with little headroom, or even lift vertically, especially with a chunk of wood or a leather glove (which works better) as a softener to improve grip. Because people can rig it wrong by pulling across the hook for vertical picks, or by hooking the hook in and not out (where the back of the hook is forced into the material, making it impossible to fail), you can't use it anymore. Works great for fence posts btw, especially with a half hitch above it
I thought you had to have a splicing certification in order to do actual rated splicing, and I'm not sure how to obtain that or if you are required to carry insurance or some shit. I personally would feel more than comfortable splicing my own stuff, as i do for everything else. I'm sure you could even say that in tree work, which is exempt from ncco bullshit, hand spliced stuff is very common trade practice, so splicing your own is in line with industry practice. The tree industry has to fight this commercialization of rigging, because trust me, where i come from, it's a nightmare.