You're on a ski trip and you want a fleece for the lodge, a shell on the mountain, and an insulated parka for the evenings in town. This is the ideal environment for the component jacket. Every outdoor brand has their own term for it; Triclimate, Interchange, Trifecta, 3-in-1, but they all mean the same thing; a shell with a liner that zips out and can be worn separately.
The main reasons for buying a component jacket are economical and practical. As a rule, buying a similar shell and liner separately from the same brand will cost 30 to 50% more. The overall feature set of the component product won't be quite as nice as the separates, but the fit and integration will be very good. The ability to throw the shell on over top then take the whole thing off as one piece is convenient, or when space is at a premium but conditions are changing.
Deciding which component jacket is right for you will require some careful shopping, because the combinations can be confusing. The majority of component jackets have a waterproof shell, but not all. The integration system might allow other jackets from that brand to mate up, but not necessarily. A component jacket intended for skiing may have features like a powder skirt and goggle wipe that are not valuable to you, even though the liner is just what you had in mind.
The liners will closely resemble other light jackets from the brand, but may have a different feature set or style, to better match the shell. Liner options:
Acrylic Knit - least bulk and warmth, very light, good wicking
Standard fleece - excellent utility, good insulation but not very compressible
Windproof fleece - can create a 'vapor barrier' that keeps moisture inside, but liner can be a good standalone
Softshell - similar to windproof fleece but adds water resistance as standalone
High loft synthetic - warmer than previous options, good range of motion, low breathability
Down - best and lightest insulation, highly compressible, can feel very puffy
The most important decision to make early on is what liner you want, based on what you need or will wear separately. The weight and bulk of the liner will inform the fit and feel of the combination, but if you never wear the liner solo, you've lost some of the value of the component system. As of this writing, no brand has figured out a 'build your own' component jacket system at the prices they offer now, so you may end up with a liner you really like that comes with a shell you're not as excited about. If the combination really bugs you, check the rest of that brand's line- you may be able to build your own, but it will cost considerably more.
Expect that the combined jacket will feel a bit heavy and your range of motion will feel restrained, because you are wearing a lot of layers, all moving and shifting. The fit and performance are improved if you unzip the liner from the shell and zip it up separately. This will keep more heat inside the inner layers, and allow the body of the liner to move independently. Make sure to try all three variations of the jacket you like best, noting that the shell will be a more generous fit without the liner. The final decision will be made at the intersection of comfort, features, and price, but remember that while the satisfaction of savings is forgotten, the value of quality is remembered.