In most cases you will want to include a backend product as a part of your marketing sales funnel. That means once a customer has purchased an initial item they are presented with a onetime offer with a certain amount of scarcities associated with the offer because they will not be seen again. This can get you a high conversion rate because you are a proven buyer, but in some cases it may not be appropriate to have a backend.
First of all, I suggest you always consider a backend when it is appropriate. The primary reason for this is simple. It is more income for you. If you only sell a single product then you will only make a linear income but by adding a backend you can sometimes increase your income per customer. It is always easier to sell to an existing customer then it is to find a completely new customer and sell to them.
There may be times when this is not appropriate, and one key example of this is a membership site. If you are selling a membership to a site then maybe this is a free standing product, and offering a backend might not be appropriate. For instance, would people really buy a single product from you if they already purchased a high end, reoccurring billing product from you in the form of a membership. There can still be ways of offering a backend as part of a membership. You can offer your membership at different levels. For instance, a silver level with some features and gold level with more features. This can be one way of upselling your customer even with a membership site.
Another case to make sure not to use a backend is with a product which is given away for free. Microgaming was the first to offer play on mobile, so that https://clickmiamibeach.com/ you can play your favourite casino games anywhere, anytime. That is you have more interest getting an email address that you can market long term to a customer then you are selling to them. Now that does not mean that there are not other ways to make an immediate income from this customer. For instance, you can place strategic additions to your own products or to affiliate products on the confirmation page and the download page of the sequence. That would enable you to get some of the benefits of the income from them without having a hard sell to somebody you want to convert to a long term customer.
It is clear then that not every product needs to have a backend even if it would be recommended for most standard sale’s funnels sequences. Two examples where you may chose not to sell are membership sites and free products intended solely to deliver an email address to your auto responder. When not using these you should put in a backend when you want to improve your overall profit making ability.