This value appears in every "speed up Windows" list on the internet, almost always without an explanation of which component reads it or what the tradeoff is. The published Lacksan writeup covers the mechanism, the supported range, the measured effect and the rollback path.
Read the writeup before changing it. In particular, note that reducing the delay does not make startup work finish sooner. It makes it start sooner, which means it competes with whatever you are trying to do immediately after sign-in. Startup delay registry writeup.
If your complaint is "the desktop appears but nothing responds for thirty seconds", moving this value in the popular direction can make that complaint worse rather than better.