I recently had my personal system freeze up on me and I shut it down hard with the power button. When I restarted the system, Outlook complained about a corrupt OST file and recommended using the inbox repair tool to fix it. Silly me, I followed instructions. The end result was 1.5 hours of waiting and a still corrupted 7 GB OST file that wouldn't open.
An OST file is a local cache of your mailbox. It is redundant data that is already held on the server. It is not worth your time to fix it unless your connectivity to the server is very slow. Which may be relevant for remote users. I, on the other hand, can reach over and touch the server in my office.
After the failed OST repair, I got smart and removed the corrupted OST file. When I started Outlook, it recreated the missing OST file and synced everything to my desktop. Total time to resync was less than 30 minutes. Much faster than the repair attempt.
Your only potential risk in deleting the OST file is a small chance that there is a message in the Outbox that has not yet been synced to the server. This message would be lost.
For reference the OST file is located in: C:\Users\username\AppData\Local\Microsoft\Outlook