Choose temporary sharing when the file is short-lived
An expiring link is a good fit for support uploads, review files, and one-off handoff. You decide the TTL at upload time, so the file is not intended to stay around forever.
Choose attachments when inbox convenience matters most
If one person needs the file and the conversation lives fully inside email, attaching it directly may be the most convenient option.
The main trade-off
Attachments create multiple copies across multiple threads. A link gives you one upload and one reference point, but the recipient needs to open it before it expires.
If you want the link approach, start with temporary file upload or share files online.