5
Yes. they are vitally important. DO NOT EMPTY or DROP them.
XOOPS uses this tables to read the templates of your modules.
I mean the templates files for each module are in the modules/YOUR_MODULE/templates and you can customize them in your themes/YOUR_THEME/modules/YOUR_MODULE by just copy and paste them
but XOOPS will store them in the database for better performance and caching.
Then if you change/alter your templates (customization) they will replace in the database too.
There is an option in system -> preferences general preferences that said "Check templates for modifications ?" it should be No in a running website.
But if you set it to YES it will store new templates in the database.
btw, i should state that if you mistakenly EMPTY those tables you still could force XOOPS to store them in the database again.
just need to update your modules one by one. but you can not see anything (you will be blind) and you should know the direct URL for them:
eg for system module:
modules/system/admin.php?fct=modulesadmin&op=update&module=system
Hope i could explain that but as Mamba said core team can tell you the best explanation.