The simplest devices are on or off. If they are grossly oversized they cycle a lot and make homes less comfortable by pushing a huge volume of hot or cold air briefly.
Variable speed compressors are better, but blowers may not also be variable speed. So you'll get better efficiency but may still suffer a feeling of draftiness.
A properly sized variable speed unit will operate within some optimal band of efficiency and constantly output nearly the minimum necessary air volume to achieve the target temperature.
When I was shopping for a mini split recently all the models I could find seemed to be variable speed compressor and blowers, unless I was reading something wrong. So maybe this isn't an issue anymore? I oversized mine but wish I went even bigger after a cold snap we just had in the pnw this last winter.
Variable speed compressors are better, but blowers may not also be variable speed. So you'll get better efficiency but may still suffer a feeling of draftiness.
A properly sized variable speed unit will operate within some optimal band of efficiency and constantly output nearly the minimum necessary air volume to achieve the target temperature.