Texture

I had the modest notion that Tomita's "Pictures at an Exhibition" was better than an orchestrated version, though on review it was probably some combination of nostalgia and memory throwing off the rating; both are good. Or can be good. A live version could sour on account of the orchestra or the facility or the audience being off, while the Tomita recording is more or less the same, though the quality of the speakers or headphones can move the goodness knob around. In both cases the listening environment is important, like if there's a leaf blower† that's no bueno. Orchestration or more recently the synthesizer allows the composer to play around with texture, which is less possible with fewer instruments, and very limited on particular instruments. The piano or piano-forte or soft-loud more or less completely replaced the harpsichord for various reasons, one of which probably being the ability to make the notes sound differently. Synths or more accurately the mixing can easily play around with where the sound seems to be coming from (and the bass you hear? Your brain might be hallucinating that), though there are orchestrations where the players surround or even move around the audience. Texture can also apply to a harpsichord; the notes (which are more or less the same in texture) may be played one or two at a time, slowly for an "open" texture, or there could be a lot of notes at the same time and in succession, a dense texture. At worst this gets into piano roll players or "black MIDI" that most humans have a low to zero chance of being able to play. Samuel Conlon Nancarrow might be worth looking up. Texture in music could be distinct from the lower level counterpoint and harmony (or these days the perhaps neglected monody, which is a melodic line free of the usual distractions) or might be integral to a particular composition that uses timber and other auditory details to deliberate effect. "Pictures at an Exhibition" and the various renditions thereof, for example.

Some works work without texture; a Bach Partita may sound fine on a plastic kazoo, though might be improved on with better instrumentation or ochestration. In other works the texture is a more essential component: Boléro by Ravel would fare rather poorly if reduced to a snare drum and harpsichord, where you could probably only get away with two or three loops before you run out of the dynamic range of a single snare drum (orchestras might bring in a second snare drummer for the swell at the end) and different keyboards (sometimes linked via a switch) on a harpsichord. Boléro could be adapted to harpsichord though would likely need a transformative conversion, probably via improvisation or variation. Transformative conversions can also go the other way, where a piano work needs many changes to take advantage of what an orchestra can produce, something like a free translation of a work from one language and style to another.

† As someone said, "if it makes noise, has wheels, or destroys vegetation, the suburbanite owns it".