That distinction matters because the two things get blurred fairly often, especially by keepers newer to the hobby who search online for symptoms and end up adjusting husbandry based on guesswork rather than getting the animal seen. Reptiles are also good at masking illness until a condition is fairly advanced, which is exactly why waiting to see if something resolves on its own is rarely the safer option.
What a care sheet can't do, and was never meant to do, is replace a vet. Husbandry guidance covers what a healthy animal needs day to day: the right temperature gradient, appropriate substrate, correct lighting, a sensible feeding schedule. It doesn't, and shouldn't, attempt to cover what to do if an animal stops eating, shows changes in behaviour, or displays anything that looks like illness or injury.
Running costs are the part most new keepers underestimate. Electricity for heating and lighting runs continuously, bulbs and elements need periodic replacement, and livefood or fresh produce is an ongoing weekly cost rather than a one-off. Taken together, these typically add up to a modest but real monthly outlay, on top of the initial setup, for as long as the animal is kept.
Finding a vet with that specific experience before it's needed, rather than searching in a hurry once something's wrong, is worth doing early on. Most areas have at least one practice that sees reptiles regularly, and Reptile Centre UK it's a far better position to be in than trying to find one for the first time during an emergency.
The main problem with sourcing components separately is compatibility. A heat mat bought from one retailer might not be sized correctly for a vivarium bought from another. A thermostat's probe might not reach the right spot in a taller enclosure. Lighting fittings vary in size and mounting style between manufacturers, and substrate depth requirements differ depending on which enclosure and species combination is being used. None of these mismatches are usually dangerous on their own, but taken together they add up to a setup that never quite works as intended, and working out where a problem sits when everything came from different places is much harder.
Reptiles are often bought on the strength of how they look as juveniles, without much thought for what keeping them actually involves five or ten years down the line. Before choosing a species, it's worth weighing up lifespan, enclosure space and ongoing running costs honestly, since all three tend to outlast the initial enthusiasm of the first few weeks.