If the quilt top will lay flat, then starting on one end isn't a problem. However if it's more of a "tent" then you have to be careful to keep it straight and ease the fullness as you go.
One of the first quilts I did on my LA was one my Mom made 35 years ago - a Giant Dahlia. I think she never quilted it because it was about 5" wider across the middle than on the ends. One border was 2" shorter than the other end too. I fixed the border problem but had to just be careful and ease in the excess as I worked my way down the quilt. I could not do an all over pattern as I had to work the fullness between stitching. So I did motifs and let the fullness be in-between were there was no stitching. After being washed, it was fine.
That experience has made be nervous about quilting other people's tops.