Overview
When generating a custom world, changing the Biome Depth Weight causes the area around oceans and deep oceans to form large pillars and spikes that often stretch from sea level to the sky limit (256). Beach and stone beach biomes and the immediately surrounding area seem to be affected the most by these pillars and spikes, though some can be seen coming directly out of the ocean. Other land terrain (plains, forest, extreme hills, etc.) appears completely normal, though oceans do seem deeper than usual, often extending to bedrock for settings around 2-3 and above, even when not "deep ocean" biomes.

Keeping all settings default, including Biome Depth Weight at 1.000, seems to leave all terrain as it is normally. Changing other settings while leaving Biome Depth Weight at 1.000 does not produce beaches disproportionately extreme, that is, only Biome Depth Weight appears to be involved in the problem.

To reproduce
Select custom generation, change "Biome Depth Weight" setting, and find a beach or stone beach area. The world in the attached picture was produced with the seed -1039723598 and a setting of 1.401. Larger values of the setting (say, 5.041). produce more extreme terrain, but even a slight change (like 1.134) begins to create small spikes and pillars to 256. The beach (and spikes) is visible from the spawn on this world, but you can go to the area around (-100,100,100) for a better view.