Supports are an important part of a 3D printed object, especially when you need to print complex models. So when the supports fail (break) like in the picture above, it usually affects the rest of the print. Most likely, the print won’t finish successfully.
Supporting pillars, especially when using low support density, can be quite fragile and not very stable things. The taller (and thinner) the supports, the higher the danger of failure.
In places where you have big overhangs, supports should be added. Although some overhangs can be printed without supports, in many cases supports are required and the print won’t finish successfully without them. For overhang tests you can download stl models here.
How to fix or prevent failing supports:
Avoid isolated support towers, cut printed object to more parts.
Reduce printing speed for supports in Slic3r, section Print settings – Speed
Use different support pattern in Slic3r, section Print setting – Support material – Pattern.
Use brim for your supports and also you can increase supports spacing in Slic3r, section Print Setting – Support material – Pattern spacing.
If you really need oly custom supports in Slic3r PE you can do your own supports.