Do weapon enhancements work all the time?

When I place an enhancement into a weapon, do I receive the effect, such as '+HP each minute' constantly, or must I equip a weapon to get the benefit.

Following on, should I put constant buff enhancements into the whip, as it's always equipped?

Enhancements have an active component and a passive component. The active one like +80% more damage with this weapon when below 30% health only triggers when you use that weapon specifically. This effect does not take place if you use another weapon. It can easily be seen with the health on attack bonus.

Then there is also the passive component, like +100% reaper form duration. This effect is always active, as long as the enhancement is placed in any weapon.

Therefore, you should get all the passive bonuses you prefer, as well as one active bonus for the weapon you prefer. If you use multiple weapons, then you should choose the active effects as they fit for the weapon and your playstyle.