I don't like the way this comes across. The metadata is doing exactly what it should be, that is, updating last-used. This feature alters the granularity at which it updates the last-used.

I would also not use language like "This can cause performance issues if you are not storing your sessions in an in-memory database" because it again makes out like this is a huge problem and infers that sessions that are not stored in memory are somehow terrible for performance. It's also not the fault of the session metabag that causes the session write, it's actually the default PHP session behaviour. The feature adjusts the frequency at which sessions are written by adjusting the granularity of the metadata updates and limits session writes. Changing the granularity at which metadata is updated in itself does not affect the session write, but it's what allows you to determine cleverly if the session data has changed or not. I know it's pedantic, but I think it really matter to be crystal clear.

```
The default behaviour of PHP session is to persist the session regardless of whether
the session data has changed or not. In Symfony, each time the session is accessed
metadata is recorded (session created/last used) which can be used to determine
session age and idle time.

If for performance reasons you wish to limit the frequency at which the session persists,
this feature can adjust the granularity of the metadata updates and persist the session
less often while still maintaining relatively accurate metadata. If other session data
is changed, the session will always persist.
```