Just a little note, all Amiga's with the ECS chipset or higher can switch modes. OCS machines cannot. It's actually one of the easiest pieces of code to write:
move.w #0,$dff1dc ;NTSC mode
move.w #$20,$dff1dc ;PAL mode
WB2.x+ have the early startup menu (both mouse buttons down while the Amiga checks it's config after a reset as stated) which allow you to control it simply by pressing a key.
If the game in question hardwires in the above code, it will of course switch to the other mode overriding your earlier selection.
A few games (off the top of my head) like Lemmings (Tab) and World Championship Boxing Manager (F9/F10) allow you to toggle the frequency ingame.
Other games which only run in one mode (generally only in PAL) usually have a main loop which waits for the screen beam to reach a certain position on the screen. In NTSC mode it never reaches that position so the game appears to freeze. These games (eg. Quest of Agravain and Dynamo) need to be slightly modified to run in the alternate mode
As for your original question Shatterhand, we "Euros" (Australia/NZ also uses PAL!) used this utility a lot for sluggish games designed for NTSC machines. 3D Pool, F/A-18 Interceptor and R-Type 2 all play a lot better in 60Hz (you do miss the panel at bottom of the screen in R-Type 2 though) and you avoid that annoying black strip at the bottom of the monitor!