This is a question about power dissipated due to radiation and ohmic heating caused by common mode current in the coaxial shielding, specifically at VHF frequencies.
When a balanced antenna (such as a yagi) is fed with unbalanced feed line (such as coax), common mode current is induced in the shield of the coax. Even with a perfect SWR (no power reflected to transmitter) common mode current results in some of the power delivered to the antenna being radiated by or dissipated in the coax shield, rather than the antenna, reducing the power radiated by the antenna itself.
My question is: in practice, for VHF frequencies, are these losses due to common mode current negligible or can using a balun noticeably decrease losses due to common mode current? For the sake of this discussion, assume a near-perfect SWR (e.g., 1:1.01).
If there is an antenna efficiency reason to use a balun, what are the pros and cons of sleeve baluns vs gamma matches vs other types?