The most common implementations of a turbocharger involve mounting the unit to the downpipe of a vehicle under the hood towards the firewall of the vehicle.
A rear mount implementation is used when there is insufficient engine bay room; it may be used in place of the stock muffler. The turbo returns the boosted air (which is pulled in from a filter mounted somewhere in the rear) to the front of the vehicle and optionally through an intercooler, and then to the intake of the engine. Wiring and oil lines must be run to the rear of the vehicle and an auxiliary oil pump must be used to return oil from the turbo to the engine. According to Horsepower TV (2/3/2007), you can expect a loss of 1 psi using a rear mount turbo, because of loss due to the long pipe routings, and also about a 100oF drop in intake air temperature. The decrease is due to the cooler exhaust gases (thus a cooler turbo unit) and the cooler intermediate pipe between the turbo and the intake. Benefits include easier maintenance because the unit is more accessible.