There are many reasons - (1) the halo effect for future rounds of funding, not to mention Demo Day itself; (2) access to absolute god-tier advisors in areas tha

There are many reasons - (1) the halo effect for future rounds of funding, not to mention Demo Day itself; (2) access to absolute god-tier advisors in areas that even though you're not a first-timer, you may not have experience with (e.g. you founded a B2B SaaS company before but now are trying a B2C thing); (3) help with hiring (YMMV on this). Also the nature of a highly focused sprint for 90 days to see if something is ready to take-off can be a great forcing function too (maybe on its own that's not compelling enough, but across these various items it seems reasonable to do it again).