YC's WaaS asks quite a number of questions that would require you to provide detailed answers.
For those that took effort to answer those questions,
1. How did you find the experience?
2. Would you do the same for other job portals i.e. not limited to YC-companies?
3. What motivates you to fill in your profile diligently?
For YC companies that use WaaS to find candidates,
1. Is it really that good?
2. What incentivizes you to keep using it? Is it the features (if so, what features?)? Is it the pool of candidates?
3. Is it really better than other ways of finding candidates (e.g. TripleByte, Hired.com, etc)?