I hate plumbing, because you install a new fixture, and think, I'll just use the old lines.
However, the old lines don't match the new fittings, so ... I'll just use the new lines included...
But the new lines don't match the old fittings, so you head to the hardware store for a new set of lines.
Then you find out that the store only has one line that matches the fittings on either end, and you have
to head to another store that doesn't have any lines to match your fittings, and you end up driving
across town in traffic, near closing time, to find one more matching line for your mis-matched fittings.
Could anything be worse?
Yes, the old valve under the sink could start leaking after fitting the new lines.