If you are asking why someone would replace servicable springs, then the answer is to obtain a different level of performance from the guns. Once upon a time, Colt Gold Cup models (target guns) were fitted with lighter than standard springs. This promoted reliability with the light target loads. Unfortunately if a shooter used a lot of ball ammo in one of these guns, they could wind up getting somewhat "battered".
When replacing recoil springs in autoloaders, keep in mind that this will affect the slide velocity, and if (like the 1911) there is a firing pin spring, it should also be replaced to match the altered slide velocity. This is why the spring makers sell them in sets.
Replacing trigger springs is one way of changing the trigger pull, without doing any (permanent) "work" on the gun. Often this can achieve the desired result, depending on the particular design of gun.
Some people also replace the magazine springs with "extra power" springs to promote reliable feeding. I have never found this to be needed, but to each his own.
As far as modern (20th century) springs taking a set, this is more myth than fact. While it is possible (particularly with poorly heat treated springs), it never seems to happen to anyone, except a "friend of a friend", or some such.
There have been verified cases of springs left fully or partially compressed for DECADES, and suffering no loss of function.