I always delete the following:
hitcircleoverlay.png
approachcircle.png
I usually delete the following:
hit 300, 100, 50 (if it's difficult to tell the difference between 300 and 100 while playing; this is usually the case in map specific skins)
I rarely delete spinners. If I'm deleting spinners, it's because they blend in way too well with the hit-circle overlays and approach circles.
I sometimes delete SB flashes if they are incredibly flashy, like http://osu.ppy.sh/s/14243 and http://osu.ppy.sh/s/11788
Side note: Due to the nature of Hard Rock and Flashlight (and probably Doubletime), these mods are quite a bit easier without a background due to the higher contrast between the (lack of) background and the followpoints and/or hitcircles.
hitcircleoverlay.png
approachcircle.png
I usually delete the following:
hit 300, 100, 50 (if it's difficult to tell the difference between 300 and 100 while playing; this is usually the case in map specific skins)
I rarely delete spinners. If I'm deleting spinners, it's because they blend in way too well with the hit-circle overlays and approach circles.
I sometimes delete SB flashes if they are incredibly flashy, like http://osu.ppy.sh/s/14243 and http://osu.ppy.sh/s/11788
Side note: Due to the nature of Hard Rock and Flashlight (and probably Doubletime), these mods are quite a bit easier without a background due to the higher contrast between the (lack of) background and the followpoints and/or hitcircles.