Is it bad to multitask frequently?
Typically no; but people, like computer systems, need a break - a chance to recover, possibly more often as they age. Computers can be replaced, people cannot -- please relax if the opportunity presents itself.
As with all computers early mainframes did not multitask (early microcomputers did not multitask, early minicomputers did not multitask, early supercomputers did not multitask). Now almost all computers multitask. Multitasking has nothing to do with the size of a computer, it is almost entirely a software feature of the OS running on the computer.