Essences and Fragments stash tab worth it?

Fragments tab - because most of the things in this don't stack, having the tab is particularly convenient. Offerings and divine vessels can take up a lot of space on their own in regular storage, then add fragments on top of that.

Essences don't "need" a tab, but they also don't organize very cleanly in a regular tab. If you plan on spending any time in standard it will easily "pay" for itself in convenience while sorting through remove-only tabs after league ends.

Having purchased one of each, I can say I've been glad to have them, albeit currency and map tab are the most convenient of all.