That one clipping layer can also be a group consisting of other masks, adjustment layers, content layers, cloned layers, and so forth 
It is important to note that groups have a “Draw Isolated” option which changes the behaviour of clipping layers (similar to the advanced blending option in Photoshop to control the clipping mask behaviour - if I recall correctly).
When the “Draw Isolated” option is turned off, the blend mode of that group is ignored. When active, the group’s blend mode affects the overall comp result.
With clipping masks, for example, two vector layers add up to behave like one overall black and white mask when this property is inactive. When active, the transparency of the child layers in the clipping mask will play a role.
“Draw Isolated” is much slower to process, though.
And what is also nice about clipping masks or layer masks: the layer properties include two addition options to affect the mask: a simple invert option, as well as a feathering control.
In any case when dealing with slow-downs in more complex comping: convert the offending comp parts to Placeholder layers. There is a reason why the developers of Photoshop opted for the Smart Object solution: just like pre-comps in After Effects Smart Objects defer and limit processing to the contents inside a Smart Object, and a static version is created in the main layer stack that does not need to be processed and updated in real time.
Same with Placeholder layers: at some point complex layer stacks will begin to slow down the layer stack processing. It is at that point that we should consider converting parts of the layer stack to Placeholder layers - just like Photoshop’s Smart Objects.
And this also explains the advantages of linking external PhotoLine files in a Placeholder layer: similar to Smart Objects that link to external PSD files, it allows us to create comps within comps within comps and also work on part s outside the main comp.
Comp(ris) ? 
…and another powerful comping trick is to link an external PNG file (for example) in a Placeholder, and then edit the placeholder content. Ensure “Save a PLD file Additionally” is checked in the Save options preferences.
Add a few layers of content, and close and save the placeholder contents. The original PNG is replaced with the new PNG version. PhotoLine senses a change in the external file layer, and updates it accordingly in the main file.
Here is the thing though: edit the placeholder layer once more. Surprise: all layers still exist! Even though a flattened PNG was saved and used to update the main!
How?! Well, with that earlier preference option PhotoLine saves a native file PLD sidecar alongside with the flattened PNG version. So the main actually uses the flattened PNG --which is incredibly light on resources-- while when we edit the contents PhotoLine automatically detects that sidecar file, and opens the native source file with all the snazzy layer comping intact.
Magic! And this also works when we simply open the PNG in PhotoLine: it will open the native source layer, and when saved, both the flattened and source sidecar files are updated.
Terrific workflow for advanced complex comping work that would bring our machines to their knees otherwise. And also for development (games) work: we work directly with the final output assets as if those are layered native source files in PhotoLine.
(p.s.: I always add PLD files to my .gitignore in Git for file versioning to ignore those. And I use a secondary local file versioning tool to create versions of those PLD binaries. Keeps my repo clean, and keeps the binaries limited and manageable.)
@ogonek You will appreciate the extended “Smart Object” functionality in PhotoLine compared to Photoshop CS6: it was only in the release following CS6 → CC (2013) that external files could be linked to Smart Objects. And in one of the releases after this the PS team introduced the option to maintain colour management and image mode for their content in Smart Objects.
All that (and more) has opened up for you with Placeholder layers in PhotoLine.
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