Spam can have adverse consequences in varying degrees. Short of being banned from a particular site altogether, spammy comments may cause particular individuals to stop following you or block you from commenting.
For example, say a connection on a social media site such as Facebook, makes a post applauding themselves for having survived their first 5k run. Several friends like the post and comment with their congratulations and encouragement. But, let's say, you comment that it would be even easier to survive the next run if they bought some Running Shoes that you have to sell through an affiliate arrangement.
Your comment is inappropriate because it is a distraction to the intended subject of the conversation. While you will not likely be banned from Facebook for having made this comment, the poster and some of the others viewing this post and its comments may decide to 'hide you', unfriend you, or perhaps even block you, because they do not want to see these types of comments. These are people that might be, when the situation was more appropriate, eager to learn about the running shoes you had to offer. But now that opportunity will never arise. You have handicapped your marketing efforts by posting a spammy comment. It might take a few of these type of comments before someone actually unfriended you or blocked you, but even one such comment can be too many. Why risk it?
Now, let's look at a different example. Imagine that a friend of yours on Facebook posted that they attempted to run their first 5k run, but had to quit early because their shoes were killing their feet. Here, the intended subject of the conversation is different. After expressing the appropriate condolences for the failed attempt and offering encouragement to try again, discussing shoes naturally follows. In this post, it would be appropriate to suggest the running shoes you have to offer. No one will likely hide you, unfriend you, or block you because of your comment here. It's all common sense.
The consequences of spam can extend much farther than losing the attention of a few people on a particular social media site, however. You can be blocked from entire ISPs. You can be included on spam lists that prevent your e-mail from getting through to most e-mail servers--and thus rendering your e-mail useless for any purpose. Some jurisdictions have monetary fines and even criminal sentences for breaking the laws prohibiting spam. It can be a serious matter above and beyond the adverse effect it has on your marketing efforts.
