WALT, or weighted average lease term, is an essential metric in the valuation of office buildings as it forecasts the stability of future cash flow.  WALT was less important back when office markets like San Francisco were seeing aggressive year over year rent growth.  Back then vacancy was worth more than leased space, the theory being a buyer could take advantage of vacant space to capture higher rent (necessary to justify inflated pricing which baked in aggressive rent growth assumptions).  However, in the broader historical context of valuation, the idea that vacancy is worth more than occupancy is antithetical to defining value.  Indeed, the more prevalent (and logical) approach to value hinges on the quality and duration of the net operating income.  Of course, this approach is less sexy as it disables a seller’s capacity to “sell the dream”.  The buyer is buying stability and yield, both of which are measurable going in.