It is a fair question, and the answer is not always the one a general contractor wants to give. For a single-trade job, hiring that trade directly is often the right call. Where it goes wrong is on projects where trades depend on each other.
The problem is sequencing. On a remodel, the electrician cannot rough in until the framing is done, the insulation cannot go in until the rough inspections pass, and the drywall cannot go up until the insulation is signed off. Each trade schedules independently, and when one slips by a week, the next has already booked another job. Two or three of those and a ten-week project becomes a five-month one.
The second problem is the gaps between scopes. Every trade prices what is clearly theirs, and the small items between them, blocking for a grab bar, patching drywall after a repipe, moving a duct three inches so the cabinet fits, belong to nobody. Someone has to notice them in advance, and on a self-managed job that someone is you.
The third is accountability after the fact. When a finished shower leaks, the tile setter points at the waterproofing and the waterproofer points at the plumber. One contract with one contractor means one party owns the result regardless of which trade caused it.
So the honest answer is this. Replacing a water heater, painting the exterior, installing floors in an empty house: hire the trade directly and save the margin. A kitchen, a bathroom, an addition, or anything involving permits and inspections in sequence: the coordination is the actual product you are buying, and it is worth what it costs.
If you do hire a general contractor, ask how they sequence the work, who your single point of contact is, and how change orders are priced. The answers will tell you quickly whether you are buying coordination or just a markup.