One mesh or multiple meshes?

Hi everybody, I am currently studying game design and I have a question that has been in my mind for a long time, It is probably super simple for someone who has more experience in 3D modeling but I am just a beginner.

My question is, when you model a game asset, does the whole object has to be a unique mesh to work properly in the game engine? For instance, if you model a sword, would you start modeling the blade by using a cube, and then model the handle with another primary shape like a cylinder? is that good practice?

I have seen some tutorials where they model weapons or some other assets starting from a cube and finishing it from that single mesh. On the other hand, I have also seen some people modeling bigger things, like a castle, having separate objects like windows, then they just place them half inside of the bigger mesh of the building, which is a separated object.

What is better? what is the good practice?

Thanks for your attention!

Assets can be multiple meshes. Poly count is what matters most.

You can start with a cube and then use a cylinder and join them later or leave them separate. When modelling, “cheating” or whatever is easiest is the best work flow.

I have same question but in example on metal plane i put Bolt on it as same mesh but not connected to plane so Will shadows ambiet occlusion etc Bug or how it should be done?

Like this tank is all small things on toplike connected to all or how to do it right?

Ps . Phone