I bet my balls that the vast majority of mechanics align everything by the marks
Many do, including whoever fitted the timing belt to my car. There were Tippex marks on all five pulleys, none of which lined up with anything! On fitting the timing tools, it was a tooth out on all four cams, probably caused by not turning the engine through and tweaking the timing. That's unforgivable because it's a basic step in fitting any timing belt/chain. I thought it was smooth and powerful but it got a lot better, and more economical, when correctly timed. All the extra marks lined up too!
Now you've watched it done with the correct tools you can see why it so much easier to do, let alone do correctly, with the tools - you don't have enough hands to hold the various springy parts to get the belt on.
If each pair of pulleys is correctly aligned(you check with the crank lock and gauge before removing the belt), the cam locks slip into place. If the engine is timed correctly, it will still be correct next time the belt is due for replacement.