Northof49:
Does serial print output halt the code during that operation or otherwise interrupt rapid processing? Does the chosen baud rate effect this?
There is a small output buffer in the Arduino, and when you use Serial.write() etc to send data to the serial port, it is appended to that buffer and transmitted in the background. However, the serial port speed is fixed (and not very high) so it is easy to send data to the serial port faster than it can be transmitted. If that happens, and once the buffer has filled up, your sketch will stop (block) inside the write()/print() call until enough data has been sent to clear space for your new data in the buffer. Because the serial port is very slow (in Arduino terms), the sketch can slow down massively when that happens.
I don't know what's causing your laptop to slow down when the Arduino sends it serial data. To understand it, you'd need to know what hardware and software was running on the PC. Any modern PC should be capable of handling serial port data at the maximum speed without any problems, but if the application that is handling the data is poorly designed then it would be easy to hit performance problems.