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While I originally made these so that they wouldn't be on by default
due to concerns over the filtering used for these leading to reduced
framerates/interactive speed, I'd since found while doing some
profiling that this isn't the case.

Rather, decreased framerates were more likely to stem from trying to
perform the checks necessary for the long-keyframe drawing when many
"child" channels are involved (affecting other channels too).

So, since these are generally useful, they are now enabled by default
:)

source/blender/editors/space_action/space_action.c

@@ -76,6 +76,8 @@ static SpaceLink *action_new(const bContext *C)
 	saction->autosnap = SACTSNAP_FRAME;
 	saction->mode= SACTCONT_DOPESHEET;
 	
+	saction->ads.filterflag |= ADS_FILTER_SUMMARY;
+	
 	/* header */
 	ar= MEM_callocN(sizeof(ARegion), "header for action");