When Windows loads its Startup file, it attempts to load every program in there at the same time. Therefore, if you have quite a lot of programs starting when Windows starts, each program will try and grab CPU time so that it can load.
If each program tries to do this at the same time, you soon notice the slow down that occurs, due to your CPU trying to help all the programs to load, and your hard disk accessing multiple files.
Startup Delayer allows you to setup how many seconds after Windows has started, to load each program.