What is the impact of having illegal clock and unconstraint clock in the design

[Altera_Forum]

Anyone can tell me what is the impact of having illegal clock and unconstraint clock reported in the timequest? 

Worst come to worst, what will be the direct impact from the hardware performance?  Thanks, fpga89

[Altera_Forum]

Worst case, it just wont work. Possibly worse, it works sometimes and then fails, then works again.

[Altera_Forum]

That's mean there is no design can allow illegal clock exist? 

I guess so...  Initially, i still thought is not a critical issue to have this...

[Altera_Forum]

What's it on? If it is something that you don't care about, then it doesn't matter. Although not ideal and maybe not "good design practice", I've seen plenty of designs with unconstrained/illegal clocks that work fine. If it needs to be constrained, then it should be constrained. W

[Altera_Forum]

Thanks a lot for you guys reply. 

I think i will need to look further to solve this problem :)