It all depends on what stock you are trading, and how much you've put down. If you've bought $5000 worth of stock. Then you can sell at 50% and 100%. If you've bought $10000+, you can divide it in 3, 4, 5+ portions.
If you are too worried about $10 commission, then in the long run you'll miss a lot of chances to sell at high.. you'll kick yourself for not selling high, then you wait for the price to go back up again, and it may never will.. then you'll lose all your profit, and once you are break even you might hold longer and lose money too.. just giving worst case scenario.
but if you sold 30% at 30% increase on top, when it drops you wont' feel as bad, and you can make better decisions whether to buy back cheaper or sell the remaining position. It's all about managing your risks.
And it depends on the stock too. Sometimes you are confident a stock will go up 300%.. in that case you you don't want to sell 30% of your shares at 30%. you will do that at 90% increase.
another thing is that most stocks don't go up parabolic.. they go up, take a breather (it dips a little), then go back up again. And many times a stock can dip 50% down before it retraces back up.. so if you can time it well, you can buy back cheaper. But it's very hard to predict when such things happen. that's why people sell portion of their position along the way as it climbs up. Then they refuel on dips ( or just take profit and ride on free shares). Remember any profit is a good profit.
