Consider one of those big Black Friday sales where there are hundreds of people lined up outside the store. When the doors are opened, they all try and cram into the store at once through the doors. This creates a jam up and problems. Once in the store, there is plenty of space for everyone. Startup Delayer works by essentially roping off some of the shoppers and making them wait a little bit before being let in. This means that less people are trying to get through the door at once which makes the overall entry smoother and faster.
Startup Delayer is a simple utility with a simple interface that has a BIG impact on your system startup. One of my complaints was that certain programs or processes were starting before they could be of any use. Then, they would generate error messages because the services they need to run weren't done starting yet, which creates even more threads trying to be run at the same time, because they are running their error routines.
Look at this example of my anti-virus program trying to get updates from the Internet before my network connection has completed. That little dot under the networking tray icon is there because my DHCP address has completed installing yet. Obviously the update has failed, the network isn't ready!
With Startup Delayer, I can keep the anti-virus program from starting until the network is ready. This both makes my overall time to system ready for input smaller, and it keeps same error message from coming up every time.