DSP+FX is a bypass mode that combines the output from the current effect with the dry input signal, without feeding the input to the effect,

This allows you to go to bypass without losing the effect "tail."

It is not the same as "spillover", which fades the previous effect out while feeding the next effect in.

The Space pedal does have a true spillover, but this is only possible because its effects use much less memory, so two effects can be combines for the short changeover period.