Come to repairs, parts are always the killer on time....as well as transportation. At least the latter can be expedited, at extortionate costs (that may be different depending on your business rationale).
Me and computers works almost like airlines and planes - if it isn't being used.... I use my computers pretty much to the death, or at least until I can no longer stretch out the time that I can actually on-sell the unit (some things you can't even give away). That explains the fate of a few of my previous systems; some others were put to pasture due to untimely demises (one motherboard was fried).
For a business which relies on a computer system, that's a different kettle of fish and a second system (plus a flexible mobile system of keeping data files in sync between them) is perfectly sound... although that can get hairy if one relies on very specific software which are either exorbitant or near impossible to obtain more than one licence.
I'm actually wondering if I could purchase a Mac system next year as a teacher and claim / salary package it under the guise of using it for teaching IT / developing resources for IT (e.g. only Mac systems are able to develop apps for iOS; need it for testing compatibility of teaching resources with possible student systems, or maybe the entire school is a Mac school). Then again, sounds way too dodgy, especially since even the cheapest Mac laptop would be nuts expensive to justify convincingly on a deductions audit.
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