The most common problems:
Version chaos: File names such as "Budget_final_v3_new_FINAL.xlsx" leave it unclear which version is the current one.
No real-time collaboration: Whoever has the file open blocks everybody else.
Susceptibility to errors: A single wrong click or a deleted formula distorts the figures unnoticed.
No access while on the road: The file sits on the server, but you are at the customer site.
Missing integration: Data has to be transferred manually between different systems. That costs time and produces errors.