I am currently leasing my M Class and both myself & the wife will be leasing our GLC's. I am getting out of the lease 5 months early on my M Class as the dealer is simply taking it in P/X for the deposit on the GLC, no penalties. The upside to leasing is you can have a new car every three years (or less), the downside is the vehicle is never yours unless you wish to pay a large 'balloon' payment after three years. Personally, I'm ready for a change after three years (my record length of car ownership is 3 1/2 years) so it works well for me. If you like to hang on to your vehicle for a long time it's probably not the best option.
As an additional aside I use my vehicle for work and get an allowance from my employer towards the vehicle which must not be more than 5 years old. This scheme works really well with lease cars. It also means you can find your car in the car park in the sea of identical saloon's...