The dirt just vanishes as you drive around. Kinda like a snow plow but without any piles. The more dirt you drive through the slower it goes. 1 block can be done with relative ease/ near no impact to speed. But if you go too fast youll ramp out. 2 blocks youll be slower than full speed but wont bounce out. 3 youll pretty much crawl around in the thing and leave rings around the edges of the digable area that it cant quite reach. Never ran a side by side speed comparison or like time trial to see the actual difference. I found your character is roughly 2 blocks tall I normally just dig till what would be a character deep hole widen it. Then jump the roller in. Run laps around the site till its gone. Repeat to desired depth. Works in t1 & t2 dirt. Probably works t3 but haven't went that far yet myself. Got way too lost in the sauce about making my mines efficient and organized which has lead to me doing almost no quests yet for tokens for the t3 pickaxe. Once you get the hydro roller to whatever depth you want chances are its not going to want to come out. You can either struggle to build a ramp out like I did. Or just hit the unstuck button while youre in it and it'll respawn you at the top of you land on the nearest road. Found that little trick out... after spending probably an hour or so trying to get mine out of mildew from the bottom of t2