For example akismet or mailchimp, they both have WP plugins as well as GF plugins. Currently for akismet i have the WP plugin but not the GF plugin.
I do have the checkbox in the settings for: Protect your form entries from spam using Akismet
Is there a reason or purpose for the GF plugins, if the WP plugin exists?
If by WP plugins you are referring to another form plugin, then no you don’t need both.
Akismet is auto installed on every Wordpress website. If your website is planning on having a lot of comments on blog post I’d recommend you keeping it. If not, I’d get rid of it.
The Gravity Forms Akismet add-on does require the Akismet plugin from the WordPress plugin directory to be installed. The basic Akismet integration is site wide. The GF add-on extends it with form specific settings so you can enable/disable the integration for specific forms and customize the field mappings.
The Gravity Forms Mailchimp add-on integrates Gravity Forms directly with Mailchimp so it doesn’t require any other plugins.
I think you understood the question better than I did. Lol (I think the original question was edited!) just kidding but maybe.