Although the LibDems advanced by about 1% in votes, they lost a few seats.
I presume it’s because Cleggmania made the LibDem focus their resources on seats that would be winnable on a 5% swing to them instead of pouring time and money into their existing seats.
It’s a huge problem with FPTP that unless you have unlimited resources, you have to guess which seats you might feasible win or lose, and then concentrate on those. If you get it wrong, it might cost you dearly.
The same applies in a different way to voters:
Nobody likes to waste their vote (apart from my father-in-law), and that means people are likely to vote tactically.
However, voting tactically means guessing which parties that the contest is really going to be between and then vote for one of them, which again means that getting it wrong will mean you’ve wasted your vote.
I really hope the LibDems will manage to use this hung parliament to achieve electoral reform!