how do you manage variables within a function? you keep everything in one .data section or you manage through altering esp?

Re-entrant code requires keeping the data local, or allocating space: recursion, multi-threaded, etc. Code re-use can benefit from keeping the data local (feels more encapsulated, just copying the code into any project and use it).

Global data is needed for visibility throughout the program, and for persistence throughout execution.

Most software needs a combination of the two approaches.

There’re such words as prologue and epilogue, and the idea behind them is so widely used that it even got into a standard set of procedure macros shipped with FASM. EBP is also there for a reason.

Until thou got stack overload error thou could keep variables anywhere. In case of growing functional of thour program (stack use) thou will have to start to economy stack resources.
In multythreading app thou will need to economy stack on needs not relative to current thread. Because stack is place for threadvars.

When deciding between global vs local variables I like to think of global variables the same way as files on a disk. If the data makes sense to be stored in a file then it can also make sense to make it global. Otherwise store it locally.

But locally doesn't always have to be on the stack. If you have a large local data set then you can also allocate memory and store it there. And remember to free it before returning to the caller.

ok