I think this saying comes from 周恩来 or is it older? I presume it means 'do 2 things at the same time'. I just think, it's hard to walk anywhere on 1 leg! Maybe it had a deeper meaning in the time of the 大跃进?
Edit: More context: the subject is 剪纸的发展： 我以为可以两条腿走路：一面抓好继承，一面去抓发展。