Age-related wear and tear, such as seized brake caliper pistons from a lack of cleaning, items not being inspected such as checks for loose bolts, rougher running due to throttle bodies not being balanced, risk of engine damage if valve clearances close up, accumulation of acid and combustion by-products in the oil, sludge forming in the filter.
Why not just learn how to do the relatively simple servicing yourself and invest in a few simple tools to do the job. Thats assuming you have somewhere under cover to work and can read a manual and use a spanner/feeler gauge and can pour oil into a filler hole.
My GSA only does about 4k a year due to a similar work/life pattern so it gets "over serviced" by myself. I own a well equipped garage plus a GS911 and Harmonizer and I am lucky to be an engineer by trade (not automotive but the same skill set).
I change the oils and filter once a year and check the valves/balance throttles, all the other stuff like brake cleaning gets done roughly every 6 months (or sooner if needed.) except for mileage/condition based items like spark plugs, tyres and alternator belt.
