A faster rocker ratio ( larger numerically) opens the valve sooner in relationship to the piston position basically keeping in mind it is doing this faster once the valve lift curve starts to "open" so to speak. It doesnt change the opening and closing point of the cam lobe of course. It kind of is like increasing duration of the cam, or at least has somewhat of the same effect as such. Again, this is changing the valve lift curve. Doing this obviously creates a much quicker opening and closing of the valve, and especially on the exhaust side, this can get very radical.It ramps the opening of the valve up faster, and hence also the closing of the valve.
You stand the chance of bouncing the valve off the seat, amongst other things that are also associated with faster valve movement. It becomes way more critical to select the proper valvetrain compenents, and especially springs. The valve springs and harmonics, clearances and such are much more sensitive at that point, and it takes more knowledge and effort to choose these parts properly and know what you really need. A valve spring that is not up to the task for a 1.7 or higher ration will do lots of damage. You cant ever assume a spring thats doing a good job on a 1.5 or 1.6 ratio to be capable of handling a 1.7. A lot of this theory and design is built into the characteristics of the cylinder heads and especially camshafts. All in all, the higher ratios are better left for the high end all out race motors and has someone involved that is experienced in them.They do have the ability to create much more stress and wear on the WHOLE valvetrain.The high end racers, Top Sportsman type guys and faster are doing frequent valve spring checking and often know beforehand if there is a problem.

Hope this helps, a bit generic, but maybe useful to some degree.