Demonology is a talent tree specializations and habbo taler it gives you massive increases to all survivability, solo capabilities, and past level 50 an immensely capable pseudo-warrior pet to boot. Initially the imp gives you a nice additional DoT, and improving it can be potentially useful at higher levels, just not while within the leveling process, not demonology. Regardless, the initial talents of choice will be demonic embrace and likely intellect, the former giving you a massive health increase and dramatically increasing the viability of life tap due to your new life pool.