It is said on page 26 of the book "Trading Volatility: Trading Volatility, Correlation, Term Structure and Skew" by Bennett (2014) that:
A rule of thumb is that the value of the OTM put sold should be approximately one-third the value of the long put (if it were significantly less, the cost saving in moving from a put to a put spread would not compensate for giving up complete protection). While selling an OTM put against a near-ATM put does benefit from selling skew (as the implied volatility of the OTM put sold is higher than the volatility of the near ATM long put bought), the effect of skew on put spread pricing is not normally that significant (far more significant is the level of implied volatility).
So basically, not only skew is needed, but it should be highly skewed? Is that what this means?
Isn't skew and IV similar in nature?