I’m going to vote LibDem (obviously) but since I live in safe Labour seat with the SNP is second, it’s not going to affect who MP is.

What it will do is increase the LibDem’s vote share across the UK. Every vote like mine helps the argument for proportional representation. The BBC have a discussion thread on this very subject, which has lots of comments in favour of change, including one by me. (Via Make My Vote Count.)