Well, only quite few of my users would see sidebar because mobile users are opening it not too often. But top tags should be defined. Majority of tag clouds are showing the most used with content and that is totally different thing than the most searched/clicked per individual or all users.
If top tags are from content it servers only needs or belief of site/admin. And then such top listing is quite close to useless for users.
There is another questionmark too. If the structure relies strongly on tags then top-list starts quite fast acting more like top categories. And is such situation overused tags in top-list starts to be as useful than the search would show hits for dog on dog-related forum.
I would still like to give decision to users and an admin would just handpick few ones as defaults.