Yes, you should put a number in the bid increment so that there will be a default value greater than the previous bid when a bidder attempts to place a bid. 

If you leave this field blank or $0.00, the bidder will see the same bid amount as the Current bid in the Your Bid field.

If they hit Place Bid without increasing the bid amount, they will receive an error message that their bid has been rejected.This could be confusing or frustrating for the bidders.  If they return and place a bid, they can place an increase with as little as 1 cent.  

Be sure to place an amount in the bid increment field to make bidding easier for your bidders. You can use small bid increments, like $1.00 if desired. The bid increment amount is usually based on the value of the item, so smaller value items have lower bid increments and higher value items have larger bid increments.