Timeslicing means that the kernel interrupts each process after some milliseconds and give control to another task. Thus, each task is given CPU processing at regular intervals. This mechanism is general but requires that the kernel can pop and push program addresses on the stack, and is thus not available on the midrange PICmicro devices. Designing processes for timeslicing is very similar to designing independent programs. Programmers find this to be natural and straight forward.
State machines are usually more complex to design than a process.
At least there are more code writing to get the definitions right. One of the reasons for this is that state machines does not require the context to be saved during a task switch. Timeslicing is done by interrupt and requires that CPU registers, stack and local workspace are saved before a new task can start execution. The second reason for the slower response is that each task executes for a predefined time period before control is given to the next task. So, when many tasks are executing, the delay becomes longer.