Chemistry apart, on many a/c, full tanks gives a chance to positively check fuel levels against gauge readings before engine start ( no chance of (a dipstick) misreading a dipstick).
Personally, I prefer to top up fuel and other fluids as part of the 'post flight / wind down / rosy glow', rather than as an additional 'pre flight wind up'.
Anyway, the Chipmunk only carries 9 gal per side, has better '2 up' CG margins with full fuel, and it's kinder on the flexible tanks to keep them full.
The fuel and oil uplift is also logged directly against the last sortie and a quick mental check of flying time/type against consumption is no bad thing (this especially applies to oil consumption on the Gipsy Major!!).