Sure.
If you do manual trading, you usually go like this:
1) You look at the chart or whatever data representation you use.
2) You think of what you will do based on your system/model.
3) Then you manually enter your order (on DOM or else) with you mouse or keyboard.
All those steps will take you what, 1, 2, 3 seconds (if your fast!!).
And I'm not even including the time is takes for you application to received and show the market data.
So, it's not a couple of hundred of milliseconds that will make a big difference in this case.
FWIW, IB round trip response time between the time a market order is sent and the time the fill is received is around 250 ms. If a faster broker exists (very probable), you will save what, 50,100, 200 ms. 100 ms substracted from 2-3 seconds will not make a big difference (percentage wise).
Manual trading is slow by definition.
But if someone is using a broker that takes many seconds to process and transmit the order to the exchange, then it's another game.