Actually, the pros outweigh the cons.

I come from the 4G63 community, where the balance shafts are spun by a small belt which rides on the crank pulley behind the timing belt. When the balance shaft belt fails, it typically takes the timing belt with it, resulting in piston-to-valve contact, resulting in a set of very expensive ash trays. On the 4G54, the balance shafts are spun by a chain in front of the timing belt, but since I didn't properly time them when I put the engine back together a couple months back, they're out of sync and are creating more vibration than normal. Being a 25 year old riding lawn mower with a windshield and doors, I'm not worried about "NVH," but I would like to ensure all the nuts and bolts on the thing stay nice and tight. No telling what could happen over time with this kind of vibration. I have to go in there anyway, might as well reduce moving parts.

A reduction in complexity is always a good bet. Removing them means less parts to fail. It also means less rotating mass (I suspect they weigh between 10-20lbs altogether), which makes the already underpowered lump a bit more lively.