Hello,
Before I started modeling classes here, I always started from a single mesh to make an object. But by following various courses I discovered that the use of several separate meshes was more advantageous sometimes. But if the object is intended for animation or a game that will not be problematic to use multiple mesh?
its highly dependendant of the end result. for example if you are modeling organics like humans, then it doesn't make sense to separate the body parts form themselves. however jacket/shirt those would be their own objects. for those you need to weight paint separatarely for animations to work.
mechanical stuff, those are generally don't bend so modeling separate parts like real world makes sense, and is easier to work with.
for games, you will export the whole model as one. so when you import it to a game engine, it will see as one object and not the separate pieces.
sometimes, you actually might want to export things to a game engine separate, but again, its highly situational based.
basic rule is, if it works, use it. :)