No, dont 'top it' DURING flower! Usually the 'top' makes the fattest bud on the whole plant. If you 'top' it 2-3 weeks BEFORE flowering it'll get all branchy.

You can sometimes harvest more by 'topping' than you would normally but in some strains it just spreads out the buds instead of one big one on top and you get about the same or less bud from the branches.