Yes, many WordPress sites are indexed by search engines without the use of SEO plugins. However, using an SEO plugin can help you optimize your website for search engines, which can increase your visibility and ranking.
The importance of optimizing your site for search engines depends on several factors, including your target audience, your competition, and the keywords you're targeting. In general, it's a good idea to use an SEO plugin to help you streamline your optimization efforts and ensure that your site is optimized for search engines.
Editing your website's code, including the title tags and meta descriptions, can help improve your site's search engine optimization, but it's important to be cautious and avoid making any changes that could negatively affect your site's performance.
In summary, using an SEO plugin can be beneficial for your WordPress site's search engine optimization, but it's not necessary for your site to be indexed. It's a good idea to use a plugin to help you optimize your site, but it's also important to be careful when making any changes to your site's code.