It does matter where the boronate is placed.
2-boronate pyridines and 2-fluoro-arylboronates are unstable.
The propenyl boronic acid/ester are "stable" as you can buy them, but they are prone to proto-deborylation. I am using it in my synthesis of [confidential drug molecule].
Further, Sp2 to Sp3Sp3couplings can be difficult to do because of proto-deborylation and the potential for hydride shifts/beta hydride eliminations on alkyl chains.