You only need multiple campaigns if you have want to run different sets of ads on different budgets, or with different langauge settings.
Most likely, you should be thinking about which different ad groups you need. In general, having a few large ad groups is easier to set up, but the disadvantage is that you will have a diverse set of keywords in a single ad group, so you will not be able to write ad text that is uniquely relevant to the user's keyword. In contrast, having a greater number of small ad groups allow to group keywords into tight semantic clusters of very similar words, and then write ads that are very specific to that topic. The downside, of course, is that this is more effort, and involves writei more ads.
So, you have to find a balance between specificity and time savings. A good rule of thumb is that for every distinct landing page that you want to use, you should have a separate ad group, which contains keywords and ads that are specific to that page.
Categorized as: