Not necessarily, most likely you will not see a difference in the speed of your system.

Having said that, a P4 with WindowsXP is listed as a minimum requirement, so that counts as almost any computer that you might find today (P4 would most likely be already painfully slow for daily use, but if you have one hanging around, this is one way to waste electricity - it does its job but at the same times consumes too much electricity to do it)

I run F@h on two computers

• a top of the line i9 with 10 cores / 20 threads and a Nvidia GPU
• a NUC with a 6th Gen i5 with 2 cores / 4 threads

You can configure f@h to run only when it is free (like the time when the screensaver runs) and be idle rest of the time

F@h can be made to run all the time, but even then it runs on a low priority thread by default, which means all systems tasks get to run first and then f@h

An advanced setting is to tell F@h to run at a higher priority (this setting is not easily visible and most likely is not set to work that way)

In simple terms, it slows your computer much much much less than an antivirus does.