This may seem obvious, but with the high-quality wheels on luggage these days, we often get away with getting door to door without actually lifting the bag. A full large suitcase can be heavy and awkward to carry. Obviously, you will normally stick to the packing limit of up to 23kg, however, even at this weight a large suitcase would be hard to carry for a distance. Consider whether you have stairs at your house, or at your destination or a rough surface that the bag will need to be carried over. If you will need to carry your suitcase, consider a medium, it's a more manageable size to pick up and carry, even at maximum weight capacity.
Car boots are only so big, and one large suitcase can be all that fits in the boot. Or in the case of compact cars, taxis or other local transport, a large suitcase may not even fit. Also consider what your travel companions are taking, for 2 people, 2 large suitcases and 2 cabin suitcases, it would be questionable whether everything would all fit in a NYC cab. If you're on a tour bus, restrictions may apply anyway. And if you're heading to Greece, Africa or Asia, consider how your large suitcase will work when getting around by donkey, jeep or tuk tuk.
Similar to the previous point, but more on a logistic level. Consider being on your own, with your large suitcase and your cabin bag, attempting to hail a cab on a busy Parisian street, and attempting to load your suitcase and other gear in the rain, in a hurry, with cars honking because your blocking the traffic. It’s stressful and hard to manage – especially if you need assistance lifting the weight of the case! Same story for public transport – lugging your suitcase on to a busy subway and through crowded metro stations is seriously hard work and will have you wondering why on earth you needed that fifth pair of shoes you probably won't wear!
Large suitcases are bulky. They don't easily store in a cupboard or under the bed. If you have a small place or limited storage then consider whether you really need a large suitcase. A medium is a bit easier to manage as they can often squeeze into the top of a wardrobe or the bottom of the linen cabinet.
A full large suitcase (even the superlight ones!) is generally hovering on or over your 20-25kg limit, and no one likes an overweight fee!
If you consider the above 5 points and still think a large is the way to go, then go for it, if you can work around those issues then a large suitcase will work for you. However, if you think you may encounter issues like we’ve outlined above, the combination of a medium plus a cabin suitcase normally gives you a similar total capacity to a large suitcase, and gives you more versatility for different trips – you can take one or the other or both as needed.