Hive witness are people that come up with different ideas to make hive what it is and they contribute to the blockchain in different ways. They have different roles and if you are voting for them, it should be mostly because you like what they bring to the table and voting for them is a way of saying you like what they do.
And from what I've seen, most of the witnesses on hive are doing really well and you can support them as long as you like them but the maximum you so can vote for is thirty 30.
I hope this explains a little because this much I know, hehe
RE: Hive-Naija Weekend Engagement #54 - "Share Your Hive Knowledge"