ASIO4ALL can do real time resampling of 44.1 kHz audio to/from 48 kHz. Resampling will automatically take place whenever ASIO4ALL is opened for 44.1 kHz and the WDM driver does not support this sample rate.
There may, however, be instances in which case an audio device will support 44.1 kHz only by resampling internally. More often than not, however, this resampling quality is extremely poor and/or prone to stability issues. To work around this, you can enable this option.