Borrowing traffic can be the quickest and easiest means of generating a big surge in traffic. Using JV partners during a new product launch is the quickest, surest way of reaching the widest possible audience in the shortest possible time.
However, you need to have those JV partners available who are prepared to work with you. So never stop building relationships.
Affiliates are the best way of maximising your sales in the longer term. There are many marketers who only work as affiliates because they either have no product of their own or they can’t be bothered to create one (maybe because they’re doing just fine selling other people’s products!).
Either way, they are selling to their traffic, to their list – and not to yours. So you are borrowing their traffic for your mutual benefit.