Earlier quoted context omitted.
I buy all the groceries I need for a week. That's realistically achievable (cost, cargo capacity of my vehicle, storage capacity at home, etc.). I buy all the groceries I need from now until the end of time. That's not realistically achievable, from any perspective. Allocating all the memory you need for a day is realistically achievable. Allocating all the memory you need until the end of time is not realistically a…
The grocery analogy doesn't work. When you're "done" with a particular "grocery", it's gone. It doesn't exist anymore. When you're done using a block of memory, you can use it again and again and again. Assuming you remembered to free it. Groceries work more like write-once memory. Still sounds like a leak to me.
It's a perfectly fine way of engineering a system.
There's also a variant of this that's been used on missiles - basically, you put enough RAM on the weapon to guarantee it'll hit its target or run out of fuel before running out of memory.