If a piece is in fast 3/4 you'll tap your foot one in a bar. If it's in medium 6/8 you'll tap two in a bar. So notating the same tune at the same speed two different ways will give you the same foot taps.
there is a significant difference as i understand it in 6/8 there is more emphasis on first beat than fourth beat,in 3/4 when it is waltz time there is emphasis on first beat

But the waltz step pattern takes 6 beats - it makes no difference whether you write that as two bars of 3-time or one bar of 6-time. The earliest waltzes were usually written in 6/8 and it took decades for people to settle on 3/4 as the preferred way (probably because melodies got increasingly complicated and it's easier to subdivide longer note values).


has anyone yet mentioned Scandinavian polskas? In 3/4, but ften with a heavily accented second beat of the bar. And Guest 03.11.17 , I hadn't forgotten mazurkas, but just did not write that down. But could you expand on "not all waltzes are 3/4"? 6/8, 9/8, 12/8 or what?

Mazurkas are often written 3/4 but played 9/8. There are quite a few waltzes from north-eastern France that aren't in 3 - you get 5/8, 8/8 and 11/8.