Tagar vs walking sleep
 

Is tagar insect even worth it? Costs double the management for 10% slower mob. Just wondering I've been using it but seems like a waste

None of those is worth it imo. Mobs die way to fast to require a slow unless you have poor dps.

At lower levels (pre-50 pretty much?) stuff typically dies too fast for any slow to be worth it other than maybe Drowsy since its tiny.

Otherwise it's only useful if you're melee soloing or maaaaybe duoing.

It's a matter of figuring out the trade-off between mana saved from healing vs mana cost of slowing (factoring in resist chance). It changes depend on how hard the mob is vs the group, group dps, how much damage your tank is taking, mana regen, etc.

When in doubt throw in drowsy or walking sleep and save top slow only for very hard mobs. You should be able to develop a good strategy w/ practice. I cringe everytime I'm tanking a low blue mob, while I'm at 95% hp, in a high dps group and the shaman hits it with tugurs at 50% hp. Sometimes the mana cost of an additional nuke is better than any slow you could have cast.

If your in a group it's not worth it on regular trash mobs, if you are fighting a tough named you may as well use your best slow. If you are soloing I would cast Walking Sleep to help save mana since the difference is not that huge and you are likely fighting relatively easy/low hitting mobs to begin with if your tanking.