Just like submissives, Dominants also have limits. Though communication is wonderful and should always be part of a relationship, some Dominants will discuss their limits and may explain why they chose them, others will not.
It’s not uncommon for a Dominant to allow a friend (another Dominant) to administer a specific activity on their slave. For instance, a Dom who has an aversion to needles and thus has a limit against needle play may have a fellow Dom perform needle play on their submissive. This would allow the first Dominant to use the needle play as a reward for good behavior if the sub really enjoyed needles and as further show of their ownership.