Okay, let's take an example, an easy one.
Let' s suppose user A has 120mv, and user B has 61mv.

Let's say, there are only user A and user B in the network.

In the situation of 30 witness votes: User A will define ALL 30 top witnesses. And user B has no say at all. User B can only change the order of the top 30, but can't vote his own candidate into the top 30.

In the situation of 10 witness votes:

Two Situations:
User A will either define ALL top 10 witnesses (if he doesn't split his stake) and User B votes the remaining 10.

User A splits his stake to vote ALL top 20 witnesses. But now, user B doesn't split his stake and now has enough stake to vote his 10 people in the top 10.
(61 > 60)