Please use the correct abbreviations for SI units, case matters.
m = milli = 1e-3
M = mega = 1e6
When you say "10mhz", do you really mean 10 mHz (.01 Hz), or 10 MHz (10,000,000 Hz)? A function generator that can't go below 10 MHz wouldn't be much use for a general purpose lab instrument, but 10 mHz is fine.
As for the question in your thread title, yes a function generator that could go down to 10 Hz could be quite useful, especially if you ever get into audio work. If you never do anything but HF/VHF, then I suppose 10 MHz - 50 MHz would be alright, but that's very limiting.