A dedicated IP gives you a reputation score independent of other senders. That cuts both ways.
Use dedicated when: You send over 200,000 emails per month consistently. You have strong list hygiene. You want to isolate transactional from marketing. Your industry has higher complaint rates and you want to avoid affecting other shared-pool customers.
Stay on shared when: You send under 50,000 per month. You send inconsistently (some months high, some low). You have not yet built strong list hygiene.
The math. Mailbox providers weight reputation by volume. An IP sending 200 emails per day has barely enough signal to register any reputation at all. Splitting low volume onto a dedicated IP leaves you with too-thin signal — neither inbox-friendly nor blocklisted, just invisible.
Warmup cost. A new dedicated IP needs 14-30 days of careful warmup before reaching full send capacity. Plan for it.
The middle ground. Inbox OSS pools customers by reputation tier on shared IPs. Senders with strong hygiene share with other strong senders. This gives you most of the benefit of dedicated without the warmup cost.