I do lock or cable-tie my bags. No method is 100% effective; a determined thief can get into any bag. The point is to raise the difficulty enough to encourage casual or hurried ones to move on to another victim.

High-end luggage luggage screams that other expensive things may be inside, but plain black cheap bags are not necessarily immune.

Knowing your formerly-secured bag has been invaded as soon as it comes off the carousel allows immediate examination. Reporting theft/damage is best done before you leave the airport. It may allow opportunity to obtain replacements in a large city, before onward travel to remote areas. (In London I could replace missing insect repellent and hiking socks; in Arusha not so much.) If you wear difficult-to-find sizes, carry specialized clothing/shoes, etc., knowing immediately what's missing can greatly impact the rest of a trip.

Before TSA I never had a single theft from luggage anywhere in the world, but since they began searching bags without oversight I experience a loss every half-dozen or so flights. Boring bags, nothing checked that shouldn't be, but no recourse. TSA has even cut off locks that did not prevent access, so if I want to be able to lock my luggage en route in iffy hotels, on trains etc., I keep an extra in my carry-on.