Future proofing size constraints
I remember a discussion with a developer in the late 90's who was designing gaming software for casinos, and I remember incrediously listening to him telling me that within 20 years we will have 2 tb storage on something the size of a finger nail.
Whelp, last year (dammit, year before last, we are 2021 now) Sandisk came out with a 1 terabyte microSD card. I suppose two stacked on top of each other would meet that 2tb definition given to me in 1997, yet in the days of when high tech was a 2 gb hard drive and 16 meg of RAM, 2 tb on a postage stamp was star trek science fiction.
So, I guess we should channel both Moore and his law, and Bill Gates and his 640k is enough for anyone, and actually not try to limit ourselves - Storage is always going to be bigger, and it's going to arrive faster than we think. Flexibility is key, and if you have absolutes, make sure they are actual technical ones - like 32 bits is always going to be 2 or 4 billion depending on signing, and not arbitrary "lets set this number limit at 10 million and call it a day". It will trip you up in database ID sequences just as bad as file system design one day in the - possibly not so distant - future!