I previously use ubuntu os. But it is very difficult to find something for ubuntu then windows. And my college their use Windows. And as maximum place windows is use and maximum youtube tutorial available for Windows, I change my os to Windows. But I love Ubuntu. and for codding ubuntu is much better than windows. So I use ubuntu using flash drive to run ubuntu.
So if I use my laptop most of the time from flash drive is it harmful for my laptop ?
Running Ubuntu from a flash drive is not harmful to your computer's hardware except for the flash drive itself which is not designed ruggedly enough to take the large number of read/writes that running an operating system requires, and it will eventually wear out. I don't consider this to be much of an economic issue because USB flash drives are so inexpensive, as long as whatever data is stored on the flash drive is backed up.
Also the performance of running Ubuntu in this way is less than would be desired. Running Ubuntu from a portable external SSD has better performance than you get from a flash drives. It's smoother, more stable and there is less annoying lagging.