Housekeep expired transients from your options table
An attempt was made and lots of discussions ensued. Basically, some plugins don't use transients correctly and they use them as required storage instead of temporary cache data. This would mean any attempt by WordPress core to regularly housekeep transients may break some plugins and, hence, websites. WordPress didn't want to do this.
If you have one of these badly written plugins, yes. However, we've yet to come across anybody reporting an issue.
Yes, they implemented the clearing down of all transients upon a database upgrade. However, they don't optimise the table after, which this plugin does. So we have retained our version of this funcionality. This could mean that the WordPress may run and ours as well but, well, if it's already been cleared then the second run isn't going to do anything so it doesn't add any overheads - it just ensures the optimisation occurs, no matter what.
It runs alongside the existing trash deletion, which is timed to run once a day. However, it will also run whenever you activate the plugin, ensuring that you can immediately test the results.
This can happen when transients become "orphaned". Each transient consists of 2 record - one holds the expiry time and the other the actual data. If one is removed without the other then this will then cause problems for the scheduled housekeeping.
In this situation the Database Upgrade run, which removes all transients even if they're orphaned, will be the solution.