The "sometimes" includes the one Microsoft ships by default with Windows. It is ridiculous how much faster random file access becomes when disabling Defender's real time protection feature.
It's one of the most impactful AVs when it comes to file r/w speed, especially on lots of small files. I have no idea why I still see people calling it lighter and faster than other AV options. It's not even like the performance loss is getting better protection. Products like Bitdefender and Kaspersky have better detection rates and don't murder performance. (Personally I just turn it off and don't install a replacement)
