If you wanted to calculate TVL for a substrate chain would you include 'Reserved Balances'? Or would you only be interested in 'Locked Balances'? (Locked Balance = max lock on an account)
The difference between locked and reserve balance is that the former can be overlapping while the latter cannot. Usually reserved balance is used to lock tokens for storage consumed. When exactly something should be a lock or a reserve is an economic question. That said, you can see that reserved balance is even "more locked" than locked balance. Hence it should be included in TLV.
It depends entirely on what you want to calculate. TVL is often used as an indicator in the field of defi, and for that you'd probably need to look at attributes beyond merely locks and reserves. For example, a defi smart contract might hold funds which are not locked/reserved from the strict perspective of the Balances pallet, however they may still be logically locked into some lending/borrowing mechanism.