Soft modelling is very useful for modelling features like muscles and very small details such as wrinkles and some bumps. Soft modelling usally uses high poly models with over 250,000 faces. After you have the details you want you would create a low poly version of it with about 30,000 to 50,000 faces by baking all the details to various maps I talk about in this post and then use the low-poly version for putting in the game.
When working with soft modelling it's best to work with quads because they are not only much more easier to uv unwrap but if it's also something that will be animated, it wont distort as much.
Soft modelling is much better for modelling muscles because it's fast and can be used with references to get a very detailed model topology of human and animals.
This person show a great example of modelling muscles using soft modelling in Mudbox. He uses a reference to guide where he adds more geometry.
Another way to model is hard surface modelling where you directly control the faces, edges and vertices of the mesh. Hard surface modelling is for non-organic models such as guns, ladders, buildings ect... usually modular assets. Sometimes its useful to combine these two styles together for example using hard surface modelling to make a brick wall but then adding tonnes of detail to it by soft modelling on top of it and then baking it in to the hard surface model.
Hard surface modelling can use tries and n-gons but are still not reconmmended since it can introduce lighting artifacts etc... There are programs like instant meshes where it look at your models and retopologize it to convert all faces in to quads that look nicer and unwrap better but that can take time just because you have to export - import models.
A major difference of soft and hard modelling is that in hard modelling you are directly manipulating polygons and in soft modelling you control an area which means you have no control of each vertex or edge
