Earlier somebody asked for legitimate reasons for wanting to write low in memory, one of the perfectly valid reasons is that if allows you to use short absolute addressing.
I don't really remember which of my demos used that, but basically during development I had a 32k buffer where I copied all the lower memory on startup and then restored it on exit to avoid exploding when going back to the text editor
That's used a lot in games, of course mostly those not using TOS calls Idirect floppy access) . Coder of Wolfenstein 3D said that he used it too, but that using TOS disk access, so may be the reason for some problems (on some TOS versions).
However, using low memory - not lowest 32K, but area around $A000-$20000 is mostly done because: code is not relocatable, and they wanted that it works on 512KB machines. The result of it is failure when running from hard disk, or even just some higher TOS version. So, the reason is often just not so good code, and being not interested for hard disk run.
My opinion is that it is good to avoid TOS calls when RAM is very tight - 512K machines in first place. But when there is much more, using TOS can make it simpler. This demo case is good example for probably not good start concept. Because limited RAM it is made to use low RAM. Not only lowest 32KB. So, TOS is killed, and it uses own floppy code. Then came need for running from hard disks, and some RAM went on saving TOS workspace, hard disk driver, + needs code to swap it all. Better would be if it was designed at start to be hard disk compatible - so doing those parts of code which would be hard to make relocatable for top of 4MB RAM. Basically filling RAM from top to bottom. Then could still use TOS and hard disk driver normally (adding just some Timer settings, restores and like). If there is need for lowest 32 KB it could be swapped, as Dbug described. That would be surely much faster than swapping some 200 KB - and demo loadings would be faster. My conclusion is that main issue here was not low hard disk related, but RAM usage, and how TOS deals with RAM related.
Famous Schrodinger's cat hypothetical experiment says that cat is dead or alive until we open box and see condition of poor animal, which deserved better logic. Cat is always in some certain state - regardless from is observer able or not to see what the state is.