As a 737 and A320 pilot - I never had the luxury of FMS temperature calculations. Just 4 feet per degree above ISA per 1000' in my head.
Sea level airport, at -10ºC (ISA-25ºC) with an ILS minima of 200'. Four times 25 is 100' per 1000, so add 20' to the minima - 220 feet. Doesn't matter much at that height, but the Glide slope check passing at the Outer Marker is 1000' - and you are on an electronic glide, so at 1000' true alt. That means the "Outer Marker, Glide Slope Check OK" call (required in my manual) means a check height seen on the altimeter of 1100'. The platform altitude of 3000' at 10 miles will mean you are acutally flying at 2700' - so won't intercept the glide at 10 DME from the threshold, but at 9 DME-ish - and your terrain clearance is 300' less than indicated. For altitudes more than 5000' above the airport in these conditions, that error starts to exceed 500'. So you don't have 1000' separation from the rocks, but only 500'. And that's the reason that, in Europe at least, for MSAs above 5000' the terrain separation provided on the charts is 2000', not 1000' - it covers winter operations.
I'm using -10ºC here, because our manual only requires the calculation at -10ºC at the destination, and below.
More interestingly for me is in the Summer. Flying into a coastal Spanish airport, at 35ºC on the ground (ISA+20), there are no calculations required in the manual - but the errors have an operational effect not only in checking the glide slope, but also in capturing the GS from the platform altitude - which at these airports is high - four to seven thousand feet - as you are coming over the hills. The chart for Malaga, for instance, has you at 5000' until 14 DME, to intercept the glide. At ISA, that's perfect. At ISA+20, you are flying indicated at 5000', but are actually 400' higher than that (i.e. 5400 True Alt), so you intercept the glide at 15.3 DME or so. Now some pilots will quote the chart limit - and insist that you can't descend until 14 DME, so they will watch the glide slope slip below them, and at 14 DME will be 400' high - typically in these airports with a tail wind. Those are the ingredients for a high-speed rushed approach.
The obvious solution is to brief that you will intercept at 15.3 DME, and head on down at that distance - no problem.
You can't, of course, fly the TRUE alt of 5000' (4600 indicated) - because your ATC traffic separation is based on indicated altimetry. The VFR guy passing below may be at 4000 indicated and you'll infringe their separation...