Alignment tool explained:
With a traditional distributor you can remove the cap and grab the rotor. This way you can hold the rotor keeping it pointed at number 1
The tool is only use to provide something to grip to turn the sensor rotor while dropping the drive unit in. (keeping it pointed at number 1 so-to-speak)
The Original CMP's don't have a window in the top of the cap nor do "some" of the replacements. (Tool required). Not really. You could remove the cap and "guess" drop it in and verify, if you miss repeat until successful. (Again just like a distributor)
Some replacements DO have the "window" making your guess more educated.
The trick here is that you have to guess "practice" setting the position looking through the sight glass on top and then getting it all the way in without moving it out of range.
Ever drop a distributor only to discover that you can't get the timing right because the vacuum advance hits the fire wall or something else?
The same thing is going on here. If you don't get the orientation right you will not be able to turn it far enough to get the timing set. DUE TO THE LACK OF SPACE.
Otherwise you could stab it in any old way and just turn it till you find the voltage drop and lock it down.
Visuals:
Notice here that the distributor is all the way in and he's got the rotor pointed at the mark he made earier.
Same concept with the CMP. As the cam gear slides in it will turn the rotor a bit because it is a helical gear.
So you may have to repeat the process a couple times to get it in.
The "windowed" ones also have a mark for the actual electronic alignment but you really need verify this with the volt meter. Unless you like 10 miles per gallon.
And just like a distributor if you are way off you get spark at the wrong time and backfire out the carb.
Same thing here but were talking fuel injection timing instead of spark.
If your Waaaay off it will spray fuel at the wrong time firing the injectors too early or to late.