Campaigns can be assigned to hashtags, so when a hashtag is added to a lead for the first time, they will be assigned a specific campaign automatically.
There are a few reasons you would want to use hashtags with drip campaigns:
You want to be able to assign a contact to a drip campaign quickly and easily, while simultaneously categorizing them.
You created an advertising campaign, and you want those leads who register to be put onto a drip that is relevant to what or where you were advertising.
For the leads that are coming from a source that you hashtagged (squeeze page, landing page, etc.) you want to control the initial welcome email and/or text.
In either case, when you are configuring your drips, you'll notice a setting that will allow you to associate that campaign with a hashtag.
Assigning a hashtag to a drip campaign does two things for you.
When you assign the same hashtag to any contacts in the future (who have no existing hashtags), they will be assigned to this drip campaign immediately.The drip campaign is not applied retroactively to all contacts with that hashtag.The drip campaign will start from however old the contact is. So, if the contact is 5 days old, the drip campaign will start from the day 5 point.
If you generate a new lead from a squeeze page or landing page, or other funnel and they have that hashtag assigned, they will be put onto that campaign. Basically, it allows you to bypass whatever your default campaign is for that particular kind of lead.