Alvis, if you only work part of the year, it is useful asking to fill in a full tax form, as you will be able to use extra deductions, AND spread out your quellensteuer over the 12 months.

However, you then have to fill in a form every year as long as you stay in Switzerland (says Richard).

some of the extra deductions you can claim:

• travel to work under certain conditions
• or: a bike (700 CHF deduction)
• lunch
• some types of educational expenses
• pillar 3a (but you can use the lite form too)
• medical expenses if over 4 % of your net income (including monthly premiums perhaps; this is unclear to me)

So if you only worked part of the year, paying in the maximum of 6350 or so CHF a year is very beneficial. You can calculate how much tax roughly you will get back (go to UBS and search for calculators).