When an algorithm uses a "distance" type parameter, the units will now be shown next to the parameter. This avoids the confusion when running algorithms which use distances where the unit depends on a layer or CRS parameter - e.g. the distance parameter in the buffer algorithm gives the distance in layer units... so now in QGIS 3.2 we show those units directly within the dialog. Hopefully this leads to less user confusion and accidental "1000 degree buffers"!
Additionally - if the unit is in degrees, a small warning icon is shown next to the parameter. The tooltip for this icon advises users to reproject data into a suitable projected local coordinate system.