It doesn't hurt to have multiple campaigns, the real question is whether and why you need them. The key factor of campaigns is that it is here where budget and location targeting is set so if you have any reason to split your budget you must use separate campaigns and if you want to target different geographical regions you should consider using separate campaigns (especially if the targeting is in different countries). There's no real benefit in having more than one campaign for any other purpose, although it can still be a good idea. For example, even if you don't think you need to NOW, you may find in the future that you wish you'd split one product group into it's own campaign so you can control it's budget. As with all things Adwords, it depends... Jon
I wouldn't necessarily say you should use a new campaign for every product you promote - after all, some users could have hundreds or thousands of products. But a new campaign for each product group is probably a good idea, if only for the reasons stated above that it allows you to control the budgets for those groups.
Just 4 (there's more) reasons why you may wish to split your keywords into more than 1 Campaign: Budget: Some keywords I'm happy spending more on, so splitting them up enables me to spend more in a day on some keywords and less on others Match Types: I always have Exact match types in their own Campaigns. Plenty of threads on here as to why and I've probably posted on most of them, lol. Day of week, time of day: You can set campaigns to run at different times of day and different days of the week. Geographical: If you sell a product to 2 different countries and need Ads written in 2 languages, then you'd want to have them in 2 Campaigns.