It's a mix of security theatre (rules tend to imply that they know what they are doing when really they don't but which puts off potential aggressors and makes the general public feel safe) and reactive approaches to known risks.
-shoes taken off and scanned as a result of the shoe bomber
- larger electronics out of covers and bags after they uncovered the laptop/iPad bomb plot so they can scan properly
- liquids after they uncovered the plot to mix liquids into an explosive so they can scan properly.
None of these are really effective for someone determined but I suppose they believe it discourages it.
Easiest way is to go with it and anticipate and plan for the worst. As a frequent flyer I plan for the most stringent checks and go through the routine whether I'm asked to or not. My passage through airports is fairly painless because I plan ahead:
Pack the absolute minimum toiletries and make up. Buy shampoo, shower gel, suncream when at destination. Bring miniature perfumes, face creams etc or samples rather than big bottles. Put liquids in a separate similar sized bag at home and decant into their regulation one when there.Err on the side of caution. Assume mascara, solid foundation and eyeliner could be counted and bag it. Powders should be fine but if I have enough space in there I treat the plastic bag as my make up bag for the duration and shove everything in. Have it ready in your hand before entering security.
Once at scanning area. Toiletries bag into bin. Take out all electronics or things that look weird on a X-ray and place in their own bin so they aren't overlapping Even if you have 8 bins. Laptop, kindle, iPad, GHd's, chargers. Remove cases beforehand at home and re case later.
Clothing: avoid anything with metal bits. Don't bother wearing jewellery on your way to the airport and stash it in a zipped pocket in your bag. Safer anyway then it flying about in bins. Check your pockets before you enter security and put it all in your bag. Remove all coats, jackets, scarves, belts at the belt
Shoes. Assume they need to come off and do it at the scanning area, so wear easy slip on shoes. I even take off flip flops now. It's just easier.
Plan plan plan. Use a bag that has compartments. Put all things that need to come out into one compartment to grab them quickly. Then all you need to do is remove jackets and shoes and you are done.
If you want to really be a ninja then ensure your bins come down in the order of: things that need to go back in your compartment bag first. Collect them up, then the bag appears. Pack it all immediately and quickly and take your bin with your clothes to the side. Re dress. Pick up bag and you are done.
I also see after see people flapping about with their passport and boarding pass at security. You don't need it at the scanning area. It will have been done before security so stash it in your bag in a safe accessible place so you aren't flapping when you get asked for it at Duty Free or at the gate.