Focal therapy (FT) for the treatment of localized prostate cancer offers an alternative strategy for men seeking active treatment. Although relatively new, existing studies suggest that the majority of men who undergo FT tend to maintain levels of genito-urinary function that are indistinguishable from their pre-treatment status. However, as part of the shared decision making process, men need to balance good tolerability against a greater risk of recurrence given that much of the prostate remains intact after FT. In order to explore this trade-off, we used decision modelling. Our findings show that the burden of functional complications associated with radical prostatectomy (RP) is considerable, as an average of 243 days of perfect health are lost per patient due to treatment-induced urinary incontinence and erectile dysfunction. Given this effectiveness gap in current care, we explored by how much mortality - as worst-case outcome of disease progression - could increase to still result in net health benefit. To do this we mapped the net health benefit/loss of FT, in comparison to RP, for different levels of function preservation and increases in mortality. We believe our modelling exercise might help inform future studies that seek to enhance our understanding of how men make treatment decisions.