What are these fields in ASN.1 encoding of RSA
The are the $d_P$, $d_Q$ and of course $q_{inv}$ - in that order - in the Wikipedia article. As you can see in the formulas relating to the Chinese Remainder Theorem the primes are also used but $d$, the private exponent, isn't.

The CRT calculations can be used to speed up RSA private key operations, which are the slowest part of the RSA cryptosystem after the prime generation. The calculations also have different side channel attacks linked to them compared to "plain" RSA.