Main spring vs recoil spring

It is my understanding that a heaver recoil spring and a heaver main/hammer spring both slow the slide down during recoil.  I realize the main spring is only impacts the start of the slide motion and the recoil spring decelerates the slide at the end of travel.

What are the tradeoffs in selecting the relative weights of these springs?

Stock as designed 1911 16 pound recoil 23 pound main, I KNOW Squat. That being said IDPA- USPSA I shoot with a 21 pound main and a 15 pound recoil, power factor loads and full power factory ammo 820-900 fps , shoots nice. reduced power loads I'm shooting a 19 pound main and a 14 pound recoil also shoots very nice, I did have to swap out the "extra power" firing pin return spring with a stock one as I was getting light primer strikes,  I'm sure one of these other very learned men and women will chime in, so I am listening too.

The recoil spring’s main function is to force the slide forward and reload the firearm.  The main spring’ main function is to swing the hammer forward to strike the firing pin tho fire the round previously chambered.  

During the functioning cycle, the main spring in a 1911 pistol can be used to allow the hammer avpct as a delay to early recoil of the barrel & slide combo.   If the mainspring force is increased or the geometry of the slidestop changes to reduce the length where the hammer contacts the slide, then the delaying force goes up and this slows down the unlocking speed.  

So, increasing or decreasing the recoil spring, can be altered by changing the mainspring.  In my experience the mainspring should be changed for function only as the final tuning step.

I have heard that it is best to use at least 12# on the recoil spring to insure consistent slide lockup.  I have also heard that if you have a titanium firing pin, you need a heavier mainspring for reliable primer ignition.

I went with an 18# mainspring, that has allowed me to use a 14# recoil spring with a slide mounted H-1 size dot with low powered lead SWC loads.