The PST for Internet Calendars does not automatically compact.
Every sync is an entire, new copy saved into the PST.
I found my file is 42GB (I have about 10 calendars).
To see if you have the issue, check
If you have nothing gargantuan, then all’s well.
If your Internet Calendar Subscriptions.pst is huge:
1) you can compact it for now:
* Account Settings
* Data Files
* Click on Internet Calendar Subs
* Click on Settings
* Compact now
* It takes 4-5 seconds per meg on SSD…
2) You can change how often this downloads.
* Scroll down to Send and Receive
* Click Send/Receive button
* Edit your send/receive groups to sync Internet Calendars less frequently
3) You can set Outlook to automatically compact on close.
The drawback is that if you left it running a long time,
close might take hours. It’s also a registry change.
Because of this, I’m not listing steps for it,
but Uncle Google can help.