How To Cultivate Yam Plant Without Staking - Any Disadvantage To It?

No, you will loose over 60% of the potential return. Don't try it if you are not ready for staking.

However if you wish to, not in a marshy land. We do it here in an upland. There is a way you will trail the vines in such a way that they will spread in orderly lines on heaps. It has its own disadvantages in attendance. But, we often get good yield if other cultural practices are observed. So yes, but with low yield.

How long should stakes be; does it really matter?

You need to Stalk it for proper growth.