Walking trousers are great for year round use and are often packed with features including UV protection and a DWR...
Walking trousers are great for year round use and are often packed with features including UV protection and a DWR coating for quick rain run off if you're caught in a shower, however, this is great for summer use but they're not the warmest garment for winter use. This is where a Softshell trouser can be really useful. Softshell pants work in the same way a softshell jacket does; they're very warm and stretchy but also very breathable and most importantly windproof meaning that on cold, gusty days they will keep out any chills and allow you to keep hold of your body warmth.
In the winter, on very wet days, you can add a waterproof overtrouser such as a Berghaus Paclite or Deluge pant over normal walking trousers, but this can be a hassle; you have to carry them with you, then put them on when the rain starts and then take them off after (as they can be very unbreathable and sticky if not made of a membrane such as Gore-Tex).
Softshell trousers are, again, a great alternative if they have a membrane or laminate such as Gore Windstopper. These won't be as breathable as a softshell trouser without a membrane but they'll keep you dry in a shower. Bear in mind the seams won't be sealed so they wouldn't be classed as officially waterproof and if there's sideways rain then this might catch and seep into those unsealed zones.
The real advantage therefore is the stretch and flexibility that mens softshell trousers will offer. If you're scrambling then you need to have a wide range of movement and standard walking trousers can restrict this. Softshells to the rescue then!