I guess it would depend on what you want from your blog. If you want to help people search through your blog posts, and get the benefit of attaching some additional keywords to your posts, then it would be good to add some tags.

If you are not so interested in other people in general reading your blog, not being silly here, there is an option to block the spiders and make your blog private, then you probably don't need to add tags.

If you're making related posts then a few tags using words or phrases that your readers might search on or find interesting will make your site more navigable. Tags can help with seo but if you focus too much on that there's a good chance that you'll confuse or annoy your readers. Two or three well chosen tags will help your readers and your seo.

With the right template tags help users navigate. Do they help with SEO... likely but nothing in the world of SEO is anything but speculation based on how well one can interpret whatever data source they receive.

I would suggest to use a few related keywords as tags... there is no penalty for making your site more descriptive and user friendly to people and search engines. I use a limited number of tags on all my WordPress sites and it doesn't seem to hurt, and I want to believe it actually helps.

Tags are VERY SEO friendly. When Google spiders crawl your site and find your tags, they are added as keywords that when people searching for a specific keyword that matches one of yours, your site will be shown in the results.

Tags are a great idea. Your tags will get indexed as a page along with your actual post. For examples, you could have an entry on google such as yoursite.com/tag/marketing, as well as an entry to each post using that tag.

Tags (and categories) are WordPress' filing system. If you use them carefully and with discipline they can link related articles together very effectively.

As an example: I have a category on my site called WordPress, which contains all articles on WordPress. It's my WordPress 'folder'

But I cover lots of different aspects of WordPress, so I use tags to create subfolders within my main folder.

So articles on WordPress themes would be in the WordPress category tagged as themes and articles on WordPress plugins would be in the WordPress category and tagged as plugins.

This links related articles together, which helps both readers and the search engines find their way around - hence good for SEO.

Cheers,

Martin.