在国外看剧听歌，又不把套餐烧光

You can, provided the mobile-data quality tier is set low and the long sessions are saved for the accommodation's Wi-Fi. If you bought a plan with room for daily viewing there is nothing to worry about, but on a tightly sized plan video is the first activity to move onto Wi-Fi.

Because the app keeps adjusting resolution to the measured connection: on a strong signal it climbs to a higher tier by itself, and scenes with lots of motion cost more than static ones. Locking the quality tier makes consumption far more predictable.

It depends on that plan's own terms. Almost every plan described as unlimited states a full-speed threshold, after which the rate drops, and video feels that drop more than most activities. Read where the threshold sits and compare it with how much you really watch.

Downloads are tied to your streaming account, not to the SIM or eSIM carrying the data, so changing plans does not affect the files. If the service re-verifies periodically you still need a connection at some point, but it can come from any plan.

Audio is much lighter than video, so a full listening day is rarely the main problem, unless the highest-quality mode is switched on, which is designed for good headphones on Wi-Fi. For listening on travel data, choose the normal tier and download your regular playlists in advance.

Both major operating systems show usage broken down by app; the menu path differs by manufacturer and version but generally lives in the mobile network settings. Reset the counter on day one of the trip and the numbers will describe this trip specifically, which makes the next plan much easier to size.

Usually the app raised quality automatically on a fast connection, plus autoplay video in social apps. Disable both first.

Some services re-verify periodically, so open the app once on Wi-Fi before a long offline stretch.