Shift is known as 'walking' touh so you can't fall from a block but shift has other interests which may be from bugs or from game making. Here is a list of possibilty with shift (PS : some will prove some 'cheats' are just shift)
-When you fall from high place, wait the 1-2 last seconds and press shift! ALL hearths you had to loose with your fall are forgot cause shift considerate you on an air block cause normaly, it's how shift work. Same if you fall on a slab or on edge of a block.
- Shift is just you can stand 0.1 seconds on air and then you fall. When you're on a block, hitbox considerate you as on the block and not only on air block so you can still there without falling. That works too with water and lava like air.
-Sneak can be usefull for a fast elevator. This elevator needs full block (cobble dirt etc) and if ou want fastest, use ladders. Do 2 tower in that order (cobble - air- cobble-air...), one is in front of you and the second at your right or at your left. First tower will have this order (cobble - air-cobble-air...) and the second (air-cobble-air-cobble). Jump and sneak and elevator goes. If you want , you can go up faster with ladders on cobblestones.
-You can jump 2 blocks high with jump and shift easily.
If you have anything to ask or else, tell me, I can answer to you. (PS : shift is available on android but I don't know how it works, ask someone who made it)