"By default" means it's just a switch in the Bios to fix this issue? If yes, not a big deal, is it?
You'll lose these secrets and keys, forever. They may be private keys, decryption tokens and more.
You may not be able to regenerate them and get everything back.
Edit: Windows (license) keys are not in the TPM apparently, my bad, sorry. Keeping the above text for context correctness.
I have said may because I'm not using Windows on my systems for the last 20 years. IF they're not doing that, it's great, honestly.
I don't claim to be 100% correct, and kindly pointing that I'm wrong is enough to update my wrinkly muscle.
BitLocker uses TPM to store HDD encryption keys.
I suppose you need it to resize the partition without deleting your encrypted Windows data, at least.