Where the record lives
This is the fundamental difference. If the pipeline lives inside a mail client, adoption is easy and the record is tied to a mailbox and a browser. If the pipeline lives in its own application, there is one more place to visit and the record belongs to the business.
Team size each assumes
Inbox-based tracking is most comfortable for very small groups with high trust and simple ownership. Once several people share accounts, or a manager needs a view across everyone, a separate application is generally easier to live with.
Breadth versus depth
Depth in email context is the strength of this category, and depth in sales management is where it is thinner: forecasting, automation, scoring and campaign tooling. Decide which kind of depth your quarter actually needs.
Implementation effort
Both are quick. The hidden effort is standardisation. Inbox-based systems tend to accumulate personal conventions that only make sense to their author, which becomes expensive when someone leaves.
Channel coverage
Google-centric CRMs are excellent at email and calendar and, by design, quieter on voice and messaging. If a meaningful share of your selling happens on the phone or on WhatsApp, check carefully how each records it before you assume the timeline is complete.