In Lotto 5-4-3-2-1 how does playing different number of numbers affect game?

Sn@kebite

You can select to play first 1, 2, 3, 4 or 5 balls against the outcome.

How does this impact the game at all?

for example if I play 1 EUR on 6 number game and play 1 number it means I won't get top prize. but why would someone play less than the 5 numbers by choice.

Or I could play 1EUR and play for 3 balls etc... does this impact odds and limits top prize? What is the trade-off?

It's probably simple but i read the leaflet and it just states select number of balls to play but not what it's for.