Do obstacles slow down troops in Clash of Clans?

Keep in mind that allowing such obstacles on your base makes it much harder to switch and edit base layouts. Even tombstones from a prior attacker will prevent you from activating a base-layout without removing them or modifying and editing your layout. With that in mind, any benefits are costing you in flexibility and better base design.

Plus, obstacles also operate as gaps in the footprint of buildings, allowing attackers to place troops behind walls and closer to surrounding buildings.

Last but not least, you miss out on the gems you get from clearing them, along with XP points and bonus gems.

No obstacles don't slow down troops and if they do it would be probably like 0.000001% slower so u would have to place a lot of obstacles for it to make the slightest difference.

Although it could make troops reroute to attack some other building.