I wouldn’t agree with that. I work with models that sometimes have hundreds of parts but I still create them in the same model. I’ve never had any problems with losing my work. And I use parts I’ve drawn as references for the dimensions of parts I am drawing next. This results in less work, I don’t need to know as many dimensions to draw the model, and I find it less likely to induce errors. Fortunately there are different ways to work so if you prefer to create separate files for each part and combine them, you can do that.