It's the limits for their plans (probably a budget host).
It boils down to how CPU intensive your client's apps are and probably no Cron jobs that would take longer than that many seconds to execute (or other scripting operations) and on the low-end plan if they have a forum or a program that uses a database you can't have more than 8 users on at once. But It's not clear if that's for your entire reseller account or each resold database.
Don't know the host or the pricing but they may have crowded servers, VPS or whatever with limited resources, or just have a lower powered server for the # of accounts they put on it.
At any rate they are limiting how much CPU you can use, and how many simultaneous database connections. So if you have static sites with no databases or very limited use databases you can pick the plan accordingly. But with these type restrictions I'd be a bit leery.
Example: % CPU would depend on what type and/or how many CPU's they were running (2% of a Celeron is a lot less than 2% of a dual Xenon HT) and the % would be compared to what? Is it 2% of the maximum capacity if the CPU was running at "max" for 24 hours or 2% compared to other users...I'd ask for some explanations from them and see if you like what they say before signing up.