On the flip-side, eSIM provides some extra security for you; most people don't put a PIN-code on their SIM-card, and even if they do we've seen several attacks that break PIN-codes of SIM-cards.
This means that someone who wants to use your phone number to gain access to a service that relies on your phone number to authenticate you (too many to count), they can simply eject your SIM-card from your secure and locked phone, pop it in their own device, use it, pop it back, and you're none-the-wiser. Perhaps they turned the phone off first and there won't be any traces (visible to you anyway) that the attack even took place.
With an eSIM this attack isn't really possible, or if it is it requires much greater control over the phone, knowledge of device passcode, and is unlikely to be possible to do without alerting the target to it having happened.
So I like to keep my primary plan as an eSIM for the above reason, and having the SIM-slot free in case I want to use a local card for data only when travelling as you say (however, I find that these days I'm allowed to use my home data plan abroad without any additional fees most of the time).