It's usually fine to take the cashout, but be clear about it to your boss and the (more importantly,) taxman.
A lot of discussion here is regarding whether or not it is ethical/legal to take the cashout on the business' purchase. While it is true that in some countries this is considered a "fringe benefit" because the cash gained probably isn't any longer used for work... This in itself certainly isnt fraud.
If you were a politician in Australia booking business flights all over the country when you never intended on taking them - then getting credits later on, this has been proven as Fraud... however the other general idea that "it's already paid for, if YOU choose to cash-out your loss" is perfectly acceptible in most countries - so long as you are chalking it up to taxable fringe-benefits.
Subject example: Any popular international speaker will have a good idea of prices to travel to each country (usually business class) so when they are offered expenses to speak at a conference, they ask for the cash - and then can get there however they want. I know several University-level lecturers who are experts in their field who do this, and often downgrade so they can bring their spouse etc. The key is being clear in your tax, so that if the company gets investigated for transferring cash, it is documented that you have taken it as pay, instead. No money is being "scrubbed off the books", and you are not an Australian politician.
Speaker Troy Hunt gives many examples of why it's easier to "leave it to the speaker" to arrange their travel (etc) and most experienced event organisers are familiar with these costs also... so if it's paid to the speaker, it's what is agreed as fair, and they won't care how the cash is used so long as the speaker performs to their expectation.