First, it makes the pots extra heavy. Second, generally succulents don't get as much airflow in a car or truck and the soil won't dry out as quickly. This can quickly cause your succulents to rot.
This is one trick I wish I had learned a long time ago. I have a lot of small pots of succulents. I've had such a hard time transporting them in such a way that they stay upright during the whole move.
The type at the top left is especially nice for moving multiple pots and preventing them from tipping. So, take a look under the tables the next time you're at a nursery or ask someone if you don't see any.
I've recently started planting some of my succulents in these felt grow bags. They are awesome! It makes moving succulents so easy because the bags are very sturdy and have handles.
Big pots can be tricky to maneuver. I have two items that make moving large pots (or a lot of pots) so much easier: – A plant dolly/trolley – A flat bed cart (with attachable tub)