That one is a bit more defensible for variables, when you rename variables, it gives you "rename" or "rename all". "rename" renames the variable, leaving uses of it the same, "rename all" also renames where you used it. Deleting a variable leaves the blocks that references it in place but they'll throw an error if called (IIRC this is useful if you wanted to switch from a global to local variable or vice versa).

Now, custom blocks have a different issue, where deleting one just severs any code that was using it (so if you had some custom blocks in a program: [on start] -> a -> b -> c, deleting the definition for b will mean c no longer gets called). There's now a block to delete custom blocks, so you can make self-destructing code.