The downsides to something like this is absolutely context-dependent. But the reasons given in that post just aren't convincing. Going to Cambridge is not a "disruption" given the milestone it represents in your startup's progress. When you're a new founder with little to go in regards to beginning a company, it's the ideal scenario. For my goals, I could not think of a better use of time and energy than being involved in YC's program and working on my startup full-time.