When you press and hold the spindash button while airborne, you should immediately go into a roll when you land- the equivalent of holding down on the d-pad when you land on a slope in the classic games.
Case study: While underwater, running is subject to frictional drag. Thoking allows you to exceed that drag slightly. Spinning underwater uncaps your speed entirely. I'd like to thok onto a slope and immediately roll upon landing to preserve that aerial momentum without the floor friction kicking in. Slopes are otherwise useless for building momentum underwater.
Case study: While underwater, running is subject to frictional drag. Thoking allows you to exceed that drag slightly. Spinning underwater uncaps your speed entirely. I'd like to thok onto a slope and immediately roll upon landing to preserve that aerial momentum without the floor friction kicking in. Slopes are otherwise useless for building momentum underwater.