Equity is not a huge motivator but it's necessary in the current market because of the relative lack of cash and focus on future growth instead of present value of startups. An average engineer's long term value is easily 250k+ but most startups simply can't afford to pay that amount because a lot of that value the engineer is building won't be realized until a few years later. So a startup may instead offer $150k salary and 100k equity. No engineer in his right mind should take a $150k total comp job in Silicon Valley--to get full value (which is only fair to yourself), you can either work for a large corporation that will pay you $250k yearly income between RSU and salary or work for a startup that will pay you a smaller salary plus presumably the difference in equity.

I would much rather just take a 250k salary than a 150k plus equity if available, but I'll settle for 150k salary and 100k equity (per year) if I believe in the company and it has other appealing non-financial rewards for my service compared with megacorp.