Sequences are used to kick off multiple touchpoints and manage your opportunities through persistent followups by engaging with your contacts (prospects). They give you detailed analytics around each step and also provide with historical data for each communication.
Bulk emails, on the other hand, are one-time personalized emails sent to multiple contacts.
If you would like to track replies and auto followup with the contacts, we recommend creating a sequence. They are designed to do so and present you with the information you would need to know to plan your next steps, unlike bulk emails.
NOTE: Bulk emails that are sent out individually; thus, the other contacts on the bulk email see the email coming to them as an individual personalized email.