I mean, I guess there is no shame behind using assets that were already made beforehand but it gives the impression that you are lazy to your audience.
More often than not, your own brand is the most important, but if you are known for using free models, it could be detrimental to your image.
Itâs perfect for a reference. Itâs efficient but you might want to check for viruses.
This will not be effective if you are working for someone. If you are working for someone then I agree with what you say here.
Using photo references is much better and (in some cases easier) in my opinion. Using free models as a reference is alright though.
I believe as long as you delete the free model after youâre finished is good. Using it as a reference is an amazing idea and saves much time as you can look at sizing and other things in that asininity. Other ideas if you donât feel good using free models is using a google image to depict what youâre doing. You could copy and paste it onto a brick in-game using 2 or 3 reference pictures and also save time doing that. 
It really all depends. If you are working for someone, you should not do this. If itâs for a personal project, then thatâs fine. Personally, I like doing everything myself as itâs a lot of fun.
If you do use a free model and change it a bit (or make your own similar to another model), people will begin to see that you are getting ideas off other models, and some people take that as an offence, so be careful what you do.