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.
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.